Semiconductor device with protective element portion

ABSTRACT

In a circuit portion, a p+-type diffusion region penetrates, in the depth direction, an n−-type base region on the front side of a base substrate and surrounds a MOSFET. In a protective element portion on the same substrate, a p++-type contact region, an n+-type diffusion region, and a p+-type diffusion region are selectively provided in a p+-type diffusion region on the front side of the base substrate. The p+-type diffusion region penetrates the p−-type diffusion region in the depth direction, on the outer periphery of the p−-type diffusion region. An n+-type source region, the p+-type diffusion region, the p++-type contact region, and the n+-type diffusion region are connected to a GND terminal. The rear surface of the substrate is connected to a VCC terminal. A snapback start voltage of a parasitic bipolar element of the protective element portion is lower than that of the circuit portion.

CROSS REFERENCE TO RELATED APPLICATIONS

This is a continuation application of International ApplicationPCT/JP2016/058211 filed on Mar. 15, 2016 which claims priority from aJapanese Patent Application No. 2015-053980 filed on Mar. 17, 2015, thecontents of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The embodiments discussed herein relate to a semiconductor device and amethod of manufacturing a semiconductor device.

2. Description of the Related Art

A known power semiconductor device has a vertical power semiconductorelement and a horizontal semiconductor element for control andprotection circuits of the vertical power semiconductor element providedon a single semiconductor substrate (a semiconductor chip) to enhancereliability and achieve reductions in the size and cost of the powersemiconductor element (see, for example, Japanese Laid-Open PatentPublication Nos. 2002-359294 and 2000-91344). The structure of atraditional semiconductor device will be described taking an example ofa power semiconductor device that has provided on a single semiconductorsubstrate, a vertical n-channel power metal oxide semiconductor fieldeffect transistor (MOSFET) for an output stage and a horizontalcomplementary MOS (CMOS) for a control circuit. FIG. 13 is across-sectional diagram of the structure of the traditionalsemiconductor device.

The traditional semiconductor device depicted in FIG. 13 is an exampleof an in-vehicle, high-side power integrated circuit (IC) having avertical MOSFET 110 of a trench gate structure as a vertical n-channelpower MOSFET for the output stage. As depicted in FIG. 13, thetraditional semiconductor device includes an output stage portion, acircuit portion, and a protective element portion that protects theoutput stage portion and the circuit portion from surges, on an n-typesemiconductor base substrate (a semiconductor substrate) formed bydepositing an n⁻-type semiconductor layer 102 on a front surface of ann⁺-type supporting substrate 101. The output stage portion is providedwith the vertical MOSFET 110 for the output stage. The circuit portionis provided with the horizontal CMOS for the control circuit, and thelike. In the circuit portion, only a horizontal n-channel MOSFET 120 isdepicted of a horizontal p-channel MOSFET and the horizontal n-channelMOSFET that are complementarily connected to each other to constitute ahorizontal CMOS for the control circuit. The protective element portionis provided with a vertical diode 130 to be the protective elementportion.

In the output stage portion, the n⁺-type supporting substrate 101 andthe n⁻-type semiconductor layer 102 respectively function as a drainlayer and a drift layer. A drain electrode 109 (a drain terminal)connected to the rear surface of the base substrate (the rear surface ofthe n⁺-type supporting substrate 101) is a power source voltage terminalto which an in-vehicle battery is connected (hereinafter, referred to as“VCC terminal”). A ground terminal (hereinafter, referred to as “GNDterminal”) and an output terminal (hereinafter, referred to as “OUTterminal”) are provided on the front surface side of the base substrate(the opposite side of the n⁻-type semiconductor layer 102 from then⁺-type supporting substrate 101 side). The OUT terminal is electricallyconnected to an n⁺-type source region 107 and a p⁺⁺-type diffusionregion 108 of the vertical MOSFET 110. Reference numerals “103” to “106”respectively denote a trench, a gate insulating film, a gate electrode,and a p-type base region of the vertical MOSFET 110.

The horizontal n-channel MOSFET 120 constituting the horizontal CMOS ofthe circuit portion is arranged in a p⁻-type base region 121 selectivelyprovided in the surface layer of the front surface of the basesubstrate. In an outer periphery of the p⁻-type base region 121, ap⁺-type diffusion region 124 is provided to be away from an n⁺-typesource region 122 and an n⁺-type drain region 123 of the horizontaln-channel MOSFET 120. The depth of the p⁺-type diffusion region 124 isequal to the depth of the p⁻-type base region 121 or is deeper than thedepth of the p⁻-type base region 121. FIG. 13 depicts a case where thedepth of the p⁺-type diffusion region 124 is deeper than the depth ofthe p⁻-type base region 121. The p⁺-type diffusion region 124 functionsas an inversion preventive layer that prevents inversion of the p⁻-typebase region 121 due to the potential of a wiring layer that is depositedon the front surface of the base substrate.

In the p⁺-type diffusion region 124, a p⁺⁺-type contact region 125 isselectively provided to be a contact (an electrical contact portion)with the wiring layer. FIG. 13 depicts an example of a case where thehorizontal n-channel MOSFET 120 is used in each of various types ofinverter circuits such as a CMOS inverter, an enhanced/depletion (ED)inverter, and a resistance load inverter in the control circuit, and asource electrode connected to the n⁺-type source region 122 of thehorizontal n-channel MOSFET is electrically connected to the GNDterminal. The p⁻-type base region 121 to be a back gate is alsoelectrically connected to the GND terminal through the p⁺-type diffusionregion 124 and the p⁺⁺-type contact region 125. Reference numeral “126”denotes a gate electrode of the horizontal n-channel MOSFET 120.

The drain terminal connected to the n⁺-drain region 123 of thehorizontal n-channel MOSFET 120 is connected to circuit elements 111such as the horizontal p-channel MOSFET, a depletion MOSFET, and aresistive element, to constitute the various types of inverter circuitsin the control circuit. The circuit elements 111 are connected to ann⁺-type diffusion region 113 selectively provided in the surface layerof the front surface of the base substrate through a power sourcecircuit 112. The power source circuit 112 includes high voltage circuitelements (not depicted), receives a power source voltage potential (apotential of the VCC terminal) of the n-type semiconductor basesubstrate, and outputs a low potential to the circuit elements 111 tosupply the power source voltage to the various types of invertercircuits that are constituted by the horizontal n-channel MOSFET 120 andthe circuit elements 111. A high surge tolerance is required of thisin-vehicle power IC.

When high surge voltage such as electro-static discharge (ESD) or thelike is applied between the VCC terminal and the GND terminal, a surgesequentially intrudes in the n⁻-type semiconductor layer 102, the powersource circuit 112, the circuit elements 111, the horizontal n-channelMOSFET 120, and the GND terminal along a path from the VCC terminal, anda high voltage is applied. Of the constituent components that the surgeintrudes in, the circuit elements 111 and the horizontal n-channelMOSFET 120 each has a small size, and each of the elements as a singlecomponent has a low surge tolerance. The vertical diode 130 forabsorbing surge current (for protection from surge) is thereforeconnected in parallel between the VCC terminal and the GND terminal. Thevertical diode 130 includes a pn-junction formed by selectivelyproviding a p⁺-type diffusion region 131 in the surface layer of thefront surface of the base substrate. To avoid increases in the number ofthe process steps in forming the vertical diode 130 in the same n-typesemiconductor base substrate as that of the horizontal re-channel MOSFET120, a p⁺-type diffusion region 131 of the vertical diode 130 is formedconcurrently with the p⁺-type diffusion region 124 of the horizontaln-channel MOSFET 120.

The vertical diode 130 is subject to avalanche breakdown when surgevoltage is applied between the VCC terminal and the GND terminal, andthereby causes a current I101 to flow in the vertical direction from theVCC terminal side toward the GND terminal through the p⁺-type diffusionregion 131 and a p⁺⁺-type contact region 132 to absorb the surgecurrent. Meanwhile, a pn-junction similar to that of the vertical diode130 is formed between the p⁺-type diffusion region 124 and the n⁻-typesemiconductor layer 102 provided in the circuit portion (the region inwhich the horizontal n-channel MOSFET 120 is provided). The pn-junctionbetween the p⁺-type diffusion region 124 and the n⁻-type semiconductorlayer 102 also are subject to breakdown by an applied voltage that issubstantially equal to that for the vertical diode 130. This isequivalent to plural vertical diodes 127 whose pn-junction areas areeach smaller than that of the vertical diode 130 (hereinafter, referredto as “circuit portion diode”) being incorporated in the circuitportion, and a portion of the circuit portion occupying a large area inthe power IC being usable as the vertical diode 130 for surgeprotection. The effective pn-junction area of the vertical diode 130 forsurge protection can therefore be increased.

The breakdown current amount (the maximal current value that does notcause current breakdown) of the vertical diode 130 increases inproportion to the pn-junction area. By configuring the circuit portiondiode 127 using the portion of the circuit portion, the resistance tobreakdown of the vertical diode 130 itself can therefore be improvedrelative to a case where the vertical diode 130 is configured alone andassociated with this, the surge tolerance of the power IC can beimproved. The breakdown voltage of the vertical diode 130 is increasedwith an increase of the temperature. Even assuming that currentconcentrates at the circuit portion diode 127 that is configured usingthe portion of the circuit portion and that has a small pn-junctionarea, the breakdown voltage of the circuit portion diode 127 istherefore increased by heat generation and the concentration of thecurrent at the circuit portion diode 127 is alleviated. Local breakdownof the circuit portion therefore tends to be avoided even when thecircuit portion diodes 127 are scattered in the circuit portion asabove.

On the other hand, without limitation to the power IC, a technique isgenerally known of improving surge tolerance using a bipolar element asa protective element for surge protection instead of a diode. When abipolar element is used as a protective element for surge protection,the surge tolerance of an element to be protected is improved byimproving the capacity to absorb surge current using the snapbackproperty of the bipolar element. The snapback property of the bipolarelement depends on the device structure, and a protective elementincluding various types of bipolar structures has therefore beenproposed to improve this property (see, for examples, Japanese Laid-OpenPatent Publication Nos. 2006-93361, 2009-64974, 2011-18685, 2012-38974,2012-94797, 2012-99626, H3-49257, 2010-287909, 2010-182727, and2010-157642). In Japanese Laid-Open Patent Publication No. 2006-93361,the base width of a base layer of a bipolar ESD protective element isincreased by providing a semiconductor layer of the same semiconductortype as that of and continuous with a lower portion layer of the baselayer of the bipolar ESD protective element, to thereby improve thebreakdown voltage property of the bipolar ESD protective element itself.

In Japanese Laid-Open Patent Publication No. 2009-64974, a contactportion between a base electrode and a base region of a protectiveelement is positioned between an end on the side of a collectorelectrode of the base region and an emitter region, and a hold voltageof the protective element is thereby increased. In Japanese Laid-OpenPatent Publication No. 2011-18685, the bipolar operation of a protectiveelement is started using a breakdown of a trigger element as a trigger,and the ESD capacity and the noise tolerance are thereby improved. InJapanese Laid-Open Patent Publication No. 2012-38974, a configuration isemployed for a thyristor that is a protective element to be operatedusing a breakdown of a bipolar transistor as a trigger, and the triggervoltage is adjusted independently from the hold voltage of thethyristor. In Japanese Laid-Open Patent Publication No. 2012-94797, arecess is formed in a bottom portion of a body layer under an n⁺-typesource layer of a protective element and the snapback voltage of theprotective element is set to be lower than the snapback voltage of anelement to be protected.

In Japanese Laid-Open Patent Publication No. 2012-99626, only thetrigger voltage is adjusted without varying the hold voltage byadjusting the interval between a second conductivity type layer and abase layer provided inside the low concentration collector layer of aprotective element. In Japanese Laid-Open Patent Publication No.H3-49257, increases in the chip area are suppressed by forming on abottom surface of an impurity diffusion layer or a semiconductor layerformed in each partitioned region, a pn-junction diode whose reverseavalanche voltage is set to be higher than the normal operation voltageof a semiconductor device and to be lower than the breakdown voltages ofthe elements constituting the semiconductor device. In JapaneseLaid-Open Patent Publication No. 2010-287909, the ESD capacity and thesurge tolerance are increased by setting the resistance during abreakdown operation of a diode to be smaller than the resistance duringa breakdown operation of a transistor and setting a secondary breakdowncurrent of the diode to be larger than a secondary breakdown current ofthe transistor. Japanese Laid-Open Patent Publication Nos. 2010-182727and 2010-157642 each discloses a method of suppressing the voltage atwhich a parasitic bipolar element starts to snap back.

SUMMARY OF THE INVENTION

According to one aspect of the present invention, a semiconductor deviceincludes a first semiconductor region of a second conductivity typeselectively provided in a surface layer of a first principal surface ofa semiconductor substrate of a first conductivity type; an elementstructure of a semiconductor element provided in the first semiconductorregion; a second semiconductor region of the first conductivity typeselectively provided in the first semiconductor region, the secondsemiconductor region constituting the element structure of thesemiconductor element; a third semiconductor region of the secondconductivity type selectively provided to penetrate the firstsemiconductor region in a depth direction and to surround the elementstructure of the semiconductor element at a depth equal to or deeperthan a depth of the first semiconductor region, the third semiconductorregion having an impurity concentration that is higher than that of thefirst semiconductor region; a fourth semiconductor region of the secondconductivity type selectively provided in the surface layer of the firstprincipal surface of the semiconductor substrate to be away from thefirst semiconductor region; a fifth semiconductor region of the firstconductivity type selectively provided in the fourth semiconductorregion; a sixth semiconductor region of the second conductivity typeselectively provided to penetrate the fourth semiconductor region in thedepth direction and to be at a depth equal to or deeper than a depth ofthe fourth semiconductor region, the sixth semiconductor region havingan impurity concentration that is higher than that of the fourthsemiconductor region; a first electrode that is electrically connectedto the second semiconductor region, the third semiconductor region, thefourth semiconductor region, and the fifth semiconductor region; and asecond electrode that is connected to a second principal surface of thesemiconductor substrate.

According to another aspect of the present invention, a semiconductordevice includes a first semiconductor region of a second conductivitytype selectively provided in a surface layer of a first principalsurface of a semiconductor substrate of a first conductivity type; anelement structure of a semiconductor element provided in the firstsemiconductor region; a second semiconductor region of the firstconductivity type selectively provided in the first semiconductorregion, the second semiconductor region constituting the elementstructure of the semiconductor element; a third semiconductor region ofthe second conductivity type selectively provided in the firstsemiconductor region to surround the element structure of thesemiconductor element, the third semiconductor region having an impurityconcentration that is higher than that of the first semiconductorregion; a fourth semiconductor region of the second conductivity typeselectively provided in the surface layer of the first principal surfaceof the semiconductor substrate to be away from the first semiconductorregion; a fifth semiconductor region of the first conductivity typeselectively provided in the fourth semiconductor region; a sixthsemiconductor region of the second conductivity type selectivelyprovided in the fourth semiconductor region, the sixth semiconductorregion having an impurity concentration that is higher than that of thefourth semiconductor region; a first electrode that is electricallyconnected to the second semiconductor region, the third semiconductorregion, the fourth semiconductor region, and the fifth semiconductorregion; and a second electrode that is connected to a second principalsurface of the semiconductor substrate.

The semiconductor device further includes a seventh semiconductor regionof the second conductivity type selectively provided in the fourthsemiconductor region, the seventh semiconductor region having animpurity concentration that is higher than that of the fourthsemiconductor region. The first electrode is electrically connected tothe fourth semiconductor region through the seventh semiconductorregion. The fifth semiconductor region is arranged between the sixthsemiconductor region and the seventh semiconductor region.

The semiconductor device further includes a seventh semiconductor regionof the second conductivity type selectively provided in the fourthsemiconductor region, the seventh semiconductor region having animpurity concentration that is higher than that of the fourthsemiconductor region. The first electrode is electrically connected tothe fourth semiconductor region through the seventh semiconductorregion. The seventh semiconductor region is arranged to be away from thesixth semiconductor region. The fifth semiconductor region isselectively provided in the sixth semiconductor region.

The semiconductor device further includes a seventh semiconductor regionof the second conductivity type selectively provided in the sixthsemiconductor region, the seventh semiconductor region having animpurity concentration that is higher than that of the sixthsemiconductor region. The first electrode is electrically connected tothe fourth semiconductor region through the seventh semiconductorregion. The fifth semiconductor region is selectively provided in thesixth semiconductor region.

The semiconductor device further includes a seventh semiconductor regionof the second conductivity type selectively provided in the sixthsemiconductor region, the seventh semiconductor region having animpurity concentration that is higher than that of the sixthsemiconductor region. The first electrode is electrically connected tothe fourth semiconductor region through the seventh semiconductorregion. The fifth semiconductor region is arranged to be away from thesixth semiconductor region.

In the semiconductor device, the fifth semiconductor region is arrangedto surround a periphery of the seventh semiconductor region.

In the semiconductor device, the fifth semiconductor region is arrangedto surround a periphery of the seventh semiconductor region, and thesixth semiconductor region is arranged to surround a periphery of thefifth semiconductor region.

In the semiconductor device, the sixth semiconductor region is arrangedto surround a periphery of the seventh semiconductor region.

In the semiconductor device, the sixth semiconductor region is arrangedto surround a periphery of the fifth semiconductor region.

In the semiconductor device, the sixth semiconductor region has animpurity concentration and a depth equal to those of the thirdsemiconductor region.

In the semiconductor device, the fourth semiconductor region has animpurity concentration and a depth equal to those of the firstsemiconductor region.

According to still another aspect of the present invention, asemiconductor device includes a first semiconductor region of a secondconductivity type selectively provided in a surface layer of a firstprincipal surface of a semiconductor substrate of a first conductivitytype; an element structure of a semiconductor element provided in thefirst semiconductor region; a second semiconductor region of the firstconductivity type selectively provided in the first semiconductorregion, the second semiconductor region constituting the elementstructure of the semiconductor element; a third semiconductor region ofthe second conductivity type selectively provided to penetrate the firstsemiconductor region in a depth direction and to surround the elementstructure of the semiconductor element at a depth equal to or deeperthan a depth of the first semiconductor region, the third semiconductorregion having an impurity concentration that is higher than that of thefirst semiconductor region; a fourth semiconductor region of the secondconductivity type selectively provided in the surface layer of the firstprincipal surface of the semiconductor substrate to be away from thefirst semiconductor region; a fifth semiconductor region of the firstconductivity type selectively provided in the fourth semiconductorregion; a first electrode that is electrically connected to the secondsemiconductor region, the third semiconductor region, the fourthsemiconductor region, and the fifth semiconductor region; and a secondelectrode that is connected to a second principal surface of thesemiconductor substrate.

In the semiconductor device, a sixth semiconductor region of the secondconductivity type selectively provided in the fourth semiconductorregion, the sixth semiconductor region having an impurity concentrationthat is higher than that of the fourth semiconductor region. The firstelectrode is electrically connected to the fourth semiconductor regionthrough the sixth semiconductor region. The fifth semiconductor regionis arranged to surround a periphery of the sixth semiconductor region.

In the semiconductor device, a distance from the sixth semiconductorregion to a contact portion of the fourth semiconductor region and thefirst electrode is configured such that a first voltage at which a firstparasitic bipolar element constituted by the fifth semiconductor region,the fourth semiconductor region, and the semiconductor substrate or asecond parasitic bipolar element constituted by the fifth semiconductorregion, the sixth semiconductor region, and the semiconductor substratestarts to snap back is lower than a second voltage at which a thirdparasitic bipolar element constituted by the second semiconductorregion, the first semiconductor region, and the semiconductor substratestarts to snap back.

In the semiconductor device, a distance from the sixth semiconductorregion to the seventh semiconductor region is configured such that afirst voltage at which a first parasitic bipolar element constituted bythe fifth semiconductor region, the fourth semiconductor region, and thesemiconductor substrate or a second parasitic bipolar elementconstituted by the fifth semiconductor region, the sixth semiconductorregion, and the semiconductor substrate starts to snap back is lowerthan a second voltage at which a third parasitic bipolar elementconstituted by the second semiconductor region, the first semiconductorregion, and the semiconductor substrate starts to snap back.

In the semiconductor device, a distance from the sixth semiconductorregion to the fifth semiconductor region is configured such that a firstvoltage at which a first parasitic bipolar element constituted by thefifth semiconductor region, the fourth semiconductor region, and thesemiconductor substrate starts to snap back is lower than a secondvoltage at which a second parasitic bipolar element constituted by thesecond semiconductor region, the first semiconductor region, and thesemiconductor substrate starts to snap back.

In the semiconductor device, a distance from a corner portion of thefourth semiconductor region to a contact portion of the fourthsemiconductor region and the first electrode is configured such that afirst voltage at which a first parasitic bipolar element constituted bythe fifth semiconductor region, the fourth semiconductor region and thesemiconductor substrate starts to snap back is lower than a secondvoltage at which a second parasitic bipolar element constituted by thesecond semiconductor region, the first semiconductor region, and thesemiconductor substrate starts to snap back.

In the semiconductor device, a distance from a corner portion of thefourth semiconductor region to the sixth semiconductor region isconfigured such that a first voltage at which a first parasitic bipolarelement constituted by the fifth semiconductor region, the fourthsemiconductor region and the semiconductor substrate starts to snap backis lower than a second voltage at which a second parasitic bipolarelement constituted by the second semiconductor region, the firstsemiconductor region, and the semiconductor substrate starts to snapback.

In the semiconductor device, the fourth semiconductor region isconfigured to have an impurity concentration such that a first voltageat which a first parasitic bipolar element constituted by the fifthsemiconductor region, the fourth semiconductor region, and thesemiconductor substrate or a second parasitic bipolar elementconstituted by the fifth semiconductor region, the sixth semiconductorregion, and the semiconductor substrate starts to snap back is lowerthan a second voltage at which a third parasitic bipolar elementconstituted by the second semiconductor region, the first semiconductorregion, and the semiconductor substrate starts to snap back.

In the semiconductor device, the element structure of the semiconductorelement includes: the second semiconductor region; an eighthsemiconductor region of the first conductivity type selectively providedin the first semiconductor region and away from the second semiconductorregion; and a gate electrode that is provided through a gate insulatingfilm on a surface of the first semiconductor region at a portion betweenthe second semiconductor region and the eighth semiconductor region.

In the semiconductor device, the semiconductor device is provided withthe first semiconductor region and the fourth semiconductor regionformed at a same process step.

In the semiconductor device, the semiconductor device is provided withthe third semiconductor region and the sixth semiconductor region formedat a same process step.

In the semiconductor device, the semiconductor device is provided withthe second semiconductor region and the fifth semiconductor regionformed at a same process step.

In the semiconductor device, the semiconductor device is provided withthe third semiconductor region and the fourth semiconductor regionformed at a same process step.

The semiconductor device further includes a ninth semiconductor regionprovided between the fourth semiconductor region and the fifthsemiconductor region so as to cover the fifth semiconductor region.

In the semiconductor device, the ninth semiconductor region has animpurity concentration of the first conductivity type higher than thatof the fourth semiconductor region.

In the semiconductor device, the ninth semiconductor region has animpurity concentration of the second conductivity type higher than thatof the fourth semiconductor region.

In the semiconductor device, the fourth semiconductor region is aportion of the third semiconductor region.

The semiconductor device further includes a tenth semiconductor regionof the second conductivity type selectively provided in the surfacelayer of the first principal surface of the semiconductor substrate tobe away from the first semiconductor region and the fourth semiconductorregion; an eleventh semiconductor region of the second conductivity typeselectively provided to penetrate the tenth semiconductor region in thedepth direction and to be at a depth equal to or deeper than a depth ofthe tenth semiconductor region; and a twelfth semiconductor region ofthe second conductivity type selectively provided in a surface layer ofthe eleventh semiconductor region, the twelfth semiconductor regionhaving an impurity concentration that is higher than that of theeleventh semiconductor region. A first avalanche voltage of a firstdiode constituted by the semiconductor substrate and the thirdsemiconductor region is higher than a second avalanche voltage of asecond diode constituted by the semiconductor substrate and the eleventhsemiconductor region.

In the semiconductor device, on a surface of the first principal surfaceof the semiconductor substrate, a first distance between thesemiconductor substrate and the sixth semiconductor region is largerthan a second distance between the semiconductor substrate and theeleventh semiconductor region.

According to yet another aspect of the present invention, a method ofmanufacturing a semiconductor device including a first semiconductorregion of a second conductivity type selectively provided in a surfacelayer of a first principal surface of a semiconductor substrate of afirst conductivity type; an element structure of a semiconductor elementprovided in the first semiconductor region; a second semiconductorregion of the first conductivity type selectively provided in the firstsemiconductor region, the second semiconductor region constituting theelement structure of the semiconductor element; a third semiconductorregion of the second conductivity type selectively provided to penetratethe first semiconductor region in a depth direction and to surround theelement structure of the semiconductor element at a depth equal to ordeeper than a depth of the first semiconductor region, the thirdsemiconductor region having an impurity concentration that is higherthan that of the first semiconductor region; a fourth semiconductorregion of the second conductivity type selectively provided in thesurface layer of the first principal surface of the semiconductorsubstrate to be away from the first semiconductor region; a fifthsemiconductor region of the first conductivity type selectively providedin the fourth semiconductor region; a sixth semiconductor region of thesecond conductivity type selectively provided to penetrate the fourthsemiconductor region in the depth direction and to be at a depth equalto or deeper than a depth of the fourth semiconductor region, the sixthsemiconductor region having an impurity concentration that is higherthan that of the fourth semiconductor region; a first electrode that iselectrically connected to the second semiconductor region, the thirdsemiconductor region, the fourth semiconductor region, and the fifthsemiconductor region; and a second electrode that is connected to asecond principal surface of the semiconductor substrate, includesselectively forming the first semiconductor region and the fourthsemiconductor region to be away from each other in the surface layer ofthe first principal surface of the semiconductor substrate at a sameimpurity implantation and impurity diffusion process; selectivelyforming the second semiconductor region in the first semiconductorregion and selectively forming the fifth semiconductor region in thefourth semiconductor region at a same impurity implantation and impuritydiffusion process; and selectively forming the third semiconductorregion that penetrates the first semiconductor region in the depthdirection and selectively forming the sixth semiconductor region thatpenetrates the fourth semiconductor region in the depth direction at asame impurity implantation and impurity diffusion process.

Objects, features, and advantages of the present invention arespecifically set forth in or will become apparent from the followingdetailed description of the invention when read in conjunction with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional diagram of a structure of a semiconductordevice according to a first embodiment;

FIG. 2 is a plan diagram of a planar layout of the semiconductor deviceaccording to the first embodiment;

FIG. 3 is an explanatory diagram for explaining an operation principleof the semiconductor device according to the first embodiment;

FIG. 4 is a characteristics diagram of a snapback property of thesemiconductor device according to the first embodiment;

FIG. 5 is a cross-sectional diagram of a structure of a semiconductordevice according to a second embodiment;

FIGS. 6A and 6B are cross-sectional diagrams of a structure of asemiconductor device according to a third embodiment;

FIG. 7 is a cross-sectional diagram of a structure of a semiconductordevice according to a fourth embodiment;

FIG. 8 is a plan diagram of a planar layout of a protective elementportion of the semiconductor device according to the fourth embodiment;

FIG. 9 is a characteristics diagram of a snapback property of theprotective element portion of the semiconductor device according to thefourth embodiment;

FIGS. 10A, 10B, 10C, 10D, and 10E are cross-sectional diagrams of astructure of a semiconductor device according to a fifth embodiment;

FIG. 11 is a cross-sectional diagram of a structure of a semiconductordevice according to a sixth embodiment;

FIG. 12 is a cross-sectional diagram of another example of a structureof the semiconductor device according to the sixth embodiment;

FIG. 13 is a cross-sectional diagram of a structure of a traditionalsemiconductor device;

FIG. 14 is a cross-sectional diagram of a structure of a semiconductordevice according to a seventh embodiment;

FIG. 15 is a planar diagram of a planar layout of the semiconductordevice according to the seventh embodiment;

FIG. 16 is a characteristics diagram of the snapback property of thesemiconductor device according to the seventh embodiment;

FIG. 17 is a cross-sectional diagram of a structure of a semiconductordevice according to an eighth embodiment;

FIG. 18 is a planar diagram of a planar layout of the semiconductordevice according to the eighth embodiment;

FIG. 19 is a cross-sectional diagram of the structure of thesemiconductor device according to a ninth embodiment;

FIG. 20 is a planar diagram of the planar layout of the semiconductordevice according to the ninth embodiment;

FIG. 21 is a cross-sectional diagram of another example of the structureof the semiconductor device according to the ninth embodiment;

FIG. 22 is a cross-sectional diagram of a structure of a semiconductordevice according to a tenth embodiment;

FIG. 23 is a cross-sectional diagram of another example of a structureof the semiconductor device according to the tenth embodiment;

FIG. 24 is a cross-sectional diagram of a structure of a semiconductordevice according to an eleventh embodiment;

FIG. 25 is a planar diagram of a planar layout of the semiconductordevice according to the eleventh embodiment; and

FIG. 26 is a characteristics diagram of the snapback property of thesemiconductor device according to the eleventh embodiment.

DETAILED DESCRIPTION OF THE INVENTION

Embodiments of a semiconductor device and a method of manufacturing asemiconductor device according to the present invention will bedescribed in detail with reference to the accompanying drawings. In thepresent description and accompanying drawings, layers and regionsprefixed with n or p mean that majority carriers are electrons or holes.Additionally, + or − appended to n or p means that the impurityconcentration is higher or lower, respectively, than layers and regionswithout + or −. In the description of the embodiments below and theaccompanying drawings, main portions that are identical will be giventhe same reference numerals and will not be repeatedly described.

A structure of a semiconductor device according to a first embodimentwill be described. FIG. 1 is a cross-sectional diagram of a structure ofthe semiconductor device according to the first embodiment. FIG. 1depicts a cross-sectional view taken along a cutting line A-A′ in FIG.2. FIG. 2 is a plan diagram of a planar layout of the semiconductordevice according to the first embodiment. FIG. 2 does not depict theplanar layout of an output stage portion (similarly in FIGS. 15 and 18).The planar layout refers to the planar shapes and the arrangementconfigurations of the components as seen from a front surface side of asemiconductor substrate 100.

As an example of the semiconductor device according to the firstembodiment, FIG. 1 depicts an in-vehicle, high-side power IC that has avertical n-channel power MOSFET for the output stage, a horizontal CMOSfor a control circuit, and a protective element 30 protecting theseMOSFETs from surges, provided on a single semiconductor substrate (asemiconductor chip). In the circuit portion, only a horizontal n-channelMOSFET 20 is depicted of a horizontal p-channel MOSFET and thehorizontal n-channel MOSFET complementarily connected to each other toconstitute the horizontal CMOS for the control circuit.

For example, as depicted in FIG. 1, an output stage portion, the circuitportion, and a protective element portion are arranged away from eachother on an n-type epitaxial base substrate (the semiconductorsubstrate) formed by depositing an n⁻-type epitaxial layer 2 on thefront surface of an n⁺-type supporting substrate 1. In the output stageportion, for example, a vertical MOSFET 10 having a trench gatestructure is arranged as a vertical n-channel power MOSFET for theoutput stage. In the output stage portion, the n⁺-type supportingsubstrate 1 and the n⁻-type epitaxial layer 2 respectively function as adrain layer and a drift layer of the vertical MOSFET 10. A MOS gatestructure of the vertical MOSFET 10 is provided on the front surfaceside of the base substrate (on the opposite side of the n⁻-typeepitaxial layer 2 from the N⁺-type supporting substrate 1 side).

The MOS gate structure of the vertical MOSFET 10 is a general trenchgate structure that includes a trench 3, a gate insulating film 4, agate electrode 5, p-type base regions 6, an n⁺-type source region 7, anda p⁺⁺-type contact region 8. The planar layout of the MOS gate structureof the vertical MOSFET 10 is not depicted. The n⁺-type source region 7and the p⁺⁺-type contact region 8 are connected to a source electrode (asource terminal), and the source terminal is electrically connected toan output terminal provided on the front surface side of the basesubstrate through a wiring layer (not depicted). A drain electrode (adrain terminal (a second electrode)) 9 of the vertical MOSFET 10connected to the rear surface of the base substrate (the rear surface ofthe n⁺-type supporting substrate 1) is, for example, a power sourcevoltage potential VCC terminal.

As depicted in FIGS. 1 and 2, in the circuit portion, a horizontal CMOSfor the control circuit, the circuit elements 11, and circuits such as apower source circuit 12 are provided. For example, in the circuitportion, a p⁻-type base region (a first semiconductor region) 21 isselectively provided in the surface layer on the front surface of thebase substrate and, in the p⁻-type base region 21, an n⁺-type sourceregion (a second semiconductor region) 22 and an n⁺-type drain region(an eighth semiconductor region) 23 of the horizontal n-channel MOSFET20 constituting the horizontal CMOS for the control circuit areselectively provided away from each other. The depths of the n⁺-typesource region 22 and the n⁺-type drain region 23 may be, for example,equal to the depth of the n⁺-type source region 7 of the vertical MOSFET10.

A gate electrode 27 is provided through a gate insulating film (notdepicted) on the surface of a portion of the p⁻-type base region 21between the n⁺-type source region 22 and the n⁺-type drain region 23.The gate electrode 27 is provided in, for example, a straight-lineplanar layout. In FIG. 2, electrodes other than the gate electrode 27(the wiring layer) are not depicted. A p⁺-type diffusion region (a thirdsemiconductor region) 24 is provided that penetrates the p⁻-type baseregion 21 in the depth direction and that reaches a portion of then⁻-type epitaxial layer 2 between the p⁻-type base region 21 and then⁺-type supporting substrate 1. The p⁺-type diffusion region 24 isprovided in a vicinity of an outer periphery of the p⁻-type base region21 away from the n⁺-type source region 22 and the n⁺-type drain region23 of the horizontal n-channel MOSFET 20.

The p⁺-type diffusion region 24 is provided in, for example, asubstantially rectangular frame planar layout surrounding the peripheryof the horizontal n-channel MOSFET 20. On the inner side of the p⁺-typediffusion region 24, plural unit cells (each a functional unit of theelement) of the horizontal n-channel MOSFET 20 may be arranged. Thep⁺-type diffusion region 24 has a depth that is deeper than the depth ofthe p⁻-type base region 21, and protrudes from the lower side of thep⁻-type base region 21 (the n⁺-type supporting substrate 1 side) intothe n⁻-type epitaxial layer 2. The p⁺-type diffusion region 24 functionsas an anti-inversion layer that prevents inversion of the p⁻-type baseregion 21 caused by the potential of the wiring layer (not depicted)deposited on the front surface of the base substrate. The p⁺-typediffusion region 24 functions as a guard ring that prevents thehorizontal n-channel MOSFET 20 from being affected by a device adjacentto the horizontal n-channel MOSFET 20 such as being affected by noise.

In the p⁺-type diffusion region 24, a p⁺⁺-type contact region 25 isselectively provided that is in ohmic contact with the wiring layer (notdepicted). The p⁺⁺-type contact region 25 is provided in, for example, arectangular frame planar layout surrounding the periphery of thehorizontal n-channel MOSFET 20. The depth of the p⁺⁺-type contact region25 may be, for example, equal to the depth of the p⁺⁺-type contactregion 8 of the vertical MOSFET 10. For the snapback property of aparasitic bipolar element T2 of the circuit portion described later, aparasitic bipolar element T1 of the protective element portion merelyhas to have a predetermined snapback property (see FIG. 4), and thep⁺⁺-type contact region 25 may be omitted depending on the impurityconcentration of the p⁺-type diffusion region 24.

FIGS. 1 and 2 each depict an example of a case where the horizontaln-channel MOSFET 20 is used in each of various types of invertercircuits such as a CMOS inverter, an ED inverter, and a resistance loadinverter that constitute the control circuit in the circuit portion(similarly in FIGS. 3, 5, 11, 12, 14, 15, 17 to 19, 21, and 23). Thesource electrode (the source terminal (a first electrode)) connected tothe n⁺-type source region 22 of the horizontal n-channel MOSFET 20 iselectrically connected to a GND terminal (a GND pad) at the groundpotential that is provided on the front surface of the base substrate.For example, one contact hole 28 b constituting a contact portion 28 abetween the n⁺-type source region 22 and the wiring layer at a sourcepotential (the source electrode) is arranged to have a substantiallyrectangular planar shape.

The p⁻-type base region 21 to be a back gate is electrically connectedto the GND terminal through the p⁺-type diffusion region 24, thep⁺⁺-type contact region 25, and the wiring layer (not depicted). Forexample, plural contact holes 26 b each constituting a contact portion26 a between the p⁺⁺-type contact region 25 and the wiring layer of thehorizontal n-channel MOSFET 20, each have a substantially rectangularplanar shape and are provided to be scattered along the peripherydirection of the p⁺⁺-type contact region 25. The n⁺-type drain region 23of the horizontal n-channel MOSFET 20 is connected to the circuitelements 11 such as the horizontal p-channel MOSFET, a depletion MOSFET,and a resistive element through the drain electrode (the drain element).

The circuit elements 11 are connected to the drain terminal of thehorizontal n-channel MOSFET 20 and thereby constitute the various typesof inverter circuits. For example, one contact hole 29 b constituting acontact portion 29 a between the n⁺-type drain region 23 and the wiringlayer at a drain potential (the drain electrode) of the horizontaln-channel MOSFET 20 is arranged to have a substantially rectangularplanar shape. The circuit elements 11 are connected to a highpotential-side n⁺-type diffusion region 13 selectively provided in thesurface layer of the front surface of the base substrate through thepower source circuit 12. The power source circuit 12 includes a highvoltage circuit element (not depicted), receives a power sourcepotential of the n-type epitaxial base substrate (the potential of theVCC terminal), outputs a low potential to the circuit elements 11, andthereby supplies the power source voltage to the various types ofinverter circuits.

As depicted in FIGS. 1 and 2, the protective element portion has theprotective element 30 arranged therein that includes the vertical diode.In the protective element portion, a p⁻-type diffusion region (a fourthsemiconductor region) 31 is selectively provided away from the p⁻-typebase region 21 of the circuit portion in the surface layer of the frontsurface of the base substrate. In the p⁻-type diffusion region 31, ap⁺⁺-type contact region (a seventh semiconductor region) 32, an n⁺-typediffusion region (a fifth semiconductor region) 33, and a p⁺-typediffusion region (a sixth semiconductor region) 34 are each selectivelyprovided. The p⁺⁺-type contact region 32 is arranged in a substantiallycentral portion of the p⁻-type diffusion region 31. The p⁺⁺-type contactregion 32 is in ohmic contact with the wiring layer 35. An n⁺-typediffusion region 33 is arranged in a substantially rectangular ringplanar layout surrounding the periphery of the p⁺⁺-type contact region32.

The p⁺-type diffusion region 34 penetrates, in the depth direction, thep⁻-type diffusion region 31 near the outer periphery of the p⁻-typediffusion region 31 and reaches a portion between the p⁻-type diffusionregion 31 and the n⁺-type supporting substrate 1. The p⁺-type diffusionregion 34 is arranged, for example, more outwardly than the n⁺-typediffusion region 33 in a substantially rectangular ring planar layout tosurround the periphery of the n⁺-type diffusion region 33. The n⁺-typediffusion region 33 is arranged between the p⁺-type diffusion region 34and the p⁺⁺-type contact region 32. The n⁺-type diffusion region 33 maybe in contact with the p⁺⁺-type contact region 32 or may be arrangedaway from the p⁺⁺-type contact region 32. The p⁺-type diffusion region34 may be in contact with the n⁺-type diffusion region 33 or may bearranged away from the n⁺-type diffusion region 33. The depth of thep⁺-type diffusion region 34 is deeper than the depth of the p⁻-typediffusion region 31, and a pn-junction between the p⁺-type diffusionregion 34 and the n⁻-type epitaxial layer 2 constitutes the verticaldiode.

Preferably, the depths of the p⁻-type diffusion region 31, the p⁺⁺-typecontact region 32, the n⁺-type diffusion region 33, and the p⁺-typediffusion region 34 are, for example, respectively equal to the depthsof the p⁻-type base region 21, the p⁺⁺-type contact region 25, then⁺-type source region 22, and the p⁺-type diffusion region 24 of thecircuit portion. The reason for this is that the diffusion regions ofthe protective element portion may be formed by the same impurityimplantation and impurity diffusion step (the impurity implantation andimpurity diffusion process) as that for the diffusion regions arrangedin the circuit portion, whose conductivity types, impurityconcentrations, and depths are same as/equal to those of these diffusionregions of the protective element. Thus, even when the process variationoccurs, the extent of variation of the diffusion regions tends to be thesame in the protective element portion and the circuit portion. Theprotective element portion and the circuit portion can each therefore beadjusted to have a predetermined operation property. The cost can besuppressed because no new step needs to be added to form the protectiveelement portion and the circuit portion on the single semiconductorsubstrate.

The p⁺⁺-type contact region 32 and the n⁺-type diffusion region 33 areconnected to the GND terminal through the wiring layer 35. One or morecontact hole(s) 36 b and one or more contact hole(s) 37 b are arrangedfor the p⁺⁺-type contact region 32 and the n⁺-type diffusion region 33to constitute the contact portions 36 a and 37 a to be in contact withthe wiring layer 35. FIG. 2 depicts a state where the contact holes 36 band 37 b are each arranged in plural (black rectangular portions).Preferably, the number of the contact holes 37 b for the n⁺-typediffusion region 33 of the protective element portion to constitute thecontact portions 37 a in contact with the wiring layer 35 is greaterthan the number of the contact holes 28 b constituting the contactportions 28 a in contact with the n⁺-type source region 22 of thecircuit portion and the wiring layer (not depicted) at the sourcepotential (the ground potential). Preferably, the area of thepn-junction formed by the n⁺-type diffusion region 33 and the p⁻-typediffusion region 31 of the protective element portion is larger than thearea of the pn-junction formed by the n⁺-type source region 22 and thep⁻-type base region 21 of the circuit portion. The breakdown currentamount of the parasitic bipolar element T1 of the protective elementportion can be increased more than that of the parasitic bipolar elementT2 of the circuit portion by causing the number of the contact holes 37b, or the area of the pn-junction of the n⁺-type diffusion region 33 andthe p⁻-type diffusion region 31, or both of these to satisfy the aboveconditions in the protective element portion. For the snapback propertyof the parasitic bipolar element T2 of the circuit portion describedlater, the parasitic bipolar element T1 of the protective elementportion merely has to have a predetermined snapback property (see FIG.4), and the p⁺⁺-type contact region 32 may be omitted depending on theimpurity concentration of the p⁻-type diffusion region 31. In this case,the contact hole 37 b is formed to be in contact with the wiring layer35, in a substantially central portion surrounded by the n⁺-typediffusion region 33, of the p⁻-type diffusion region 31.

Operations of the semiconductor device according to the first embodimentwill be described. FIG. 3 is an explanatory diagram for explaining theoperation principle of the semiconductor device according to the firstembodiment. FIG. 4 is a characteristics diagram of a snapback propertyof the semiconductor device according to the first embodiment. Asdepicted in FIG. 3, vertical diodes D1 and D2 are formed by thepn-junctions between the p⁺-type diffusion regions 34 and 24, and then⁻-type epitaxial layer 2 respectively in the protective element portionand the circuit portion. An operation of the circuit portion executed ina case where the circuit portion is present alone will be described withreference to an operation principle diagram of FIG. 3 and acurrent-voltage (I-V) waveform w2 of FIG. 4. When a surge voltageintrudes from the VCC terminal, the voltage of the VCC terminal isthereby increased, and the voltage applied to the circuit portionreaches a first voltage (hereinafter, referred to as “breakdownvoltage”) Vbv2, the vertical diode D2 breaks down at the pn-junctionbetween the p⁺-type diffusion region 24 and the n⁻-type epitaxial layer2, and a current (an avalanche current) I2 starts to flow therethrough.Positive carriers (holes) generated in the vertical diode D2 due to theavalanche current I2 pass through the p⁺-type diffusion region 24 andflow from the p⁺⁺-type contact region 25 into the GND terminal throughthe wiring layer. The point of the breakdown of the vertical diode D2spreads over the entire surface of the pn-junction face between thep⁺-type diffusion region 24 and the n⁻-type epitaxial layer 2 and theregion in which the carriers are generated also spreads out as thevoltage applied to the circuit portion is increased and the avalanchecurrent I2 is increased. Associated with this, the avalanche current I2flows over a long distance until the avalanche current I2 reaches thep⁺⁺-type contact region 25 and, in the p⁺-type diffusion region 24, thevoltage drop thereof becomes significant due to the resistive componentscorresponding to the distance from the point of the breakdown to thep⁺⁺-type contact region 25. When the voltage applied to the circuitportion is further increased to a second voltage Vt2 and the avalanchecurrent I2 is increased up to a predetermined current It2, the voltagedrop in the p⁺-type diffusion region 24 exceeds a forward voltage of thepn-junction between the p⁻-type base region 21 and the n⁺-type sourceregion 22. The pn-junction between the p⁻-type base region 21 and then⁺-type source region 22 is forward-biased and a current I2 a that is acomponent of the avalanche current I2 flows toward the n⁺-type sourceregion 22 side. The current I2 a flowing toward the n⁺-type sourceregion 22 side becomes a base current, and the parasitic bipolar elementT2 including the n⁺-type source region 22, the p⁻-type base region 21,and the n⁻-type epitaxial layer 2 is turned on to snap back. In thiscase, the voltage applied to the circuit portion is reduced to a voltageVh2 that is lower than the breakdown voltage Vbv2 of the vertical diodeD2.

An operation of the protective element portion executed in a case wherethe protective element portion is present alone will be described withreference to the operation principle diagram in FIG. 3 and an I-Vwaveform w1 in FIG. 4. When a surge voltage intrudes from the VCCterminal, the voltage of the VCC terminal is thereby increased, and thevoltage applied to the protective element portion reaches a firstvoltage (the breakdown voltage) Vbv1, the vertical diode D1 breaks downat the pn-junction between the p⁺-type diffusion region 34 and then⁻-type epitaxial layer 2, and an avalanche current I1 starts to flowtherethrough. Positive carriers (holes) generated in the vertical diodeD1 due to the avalanche current I1 pass through the p⁺-type diffusionregion 34 and the p⁻-type diffusion region 31, and flow from thep⁺⁺-type contact region 32 into the GND terminal through the wiringlayer 35. The operation resistance of the vertical diode D1 isrelatively large due to a resistive component R1 by the p⁻-typediffusion region 31. When the voltage applied to the protective elementportion is further increased up to a second voltage Vt1 and theavalanche current I1 is increased up to a predetermined current It1, thevoltage drop in the p⁻-type diffusion region 31 due to the resistivecomponent R1 by the p⁻-type diffusion region 31 exceeds a forwardvoltage of the pn-junction between the p⁻-type diffusion region 31 andthe n⁺-type diffusion region 33. The pn-junction between the p⁻-typediffusion region 31 and the n⁺-type diffusion region 33 isforward-biased and a current I1 a that is a portion of the avalanchecurrent I1 flows toward the n⁺-type diffusion region 33 side. Thecurrent I1 a flowing toward the n⁺-type diffusion region 33 side becomesa base current, and the parasitic bipolar element T1 including then⁺-type diffusion region 33, the p⁻-type diffusion region 31, and then⁻-type epitaxial layer 2 is turned on to snap back. In this case, thevoltage applied to the protective element portion is reduced to avoltage Vh1 that is lower than the breakdown voltage Vbv1 of thevertical diode D1. In FIG. 3, reference numerals “I1 b” and “I2 b”denote the avalanche currents each flowing into the GND terminal throughthe wiring layer 35.

The vertical diode D1 of the protective element portion and the verticaldiode D2 of the circuit portion are compared. As to the vertical diodesD1 and D2, the breakdown voltages Vbv1 and Vbv2 thereof are equal toeach other because the conditions (the impurity concentration and thediffusion depth) are substantially equal for the p⁺-type diffusionregions 34 and 24 constituting the pn-junctions of the vertical diodesD1 and D2. On the other hand, the protective element portion and thecircuit portion differ from each other on the following two points. Thefirst point is as follows. In the circuit portion, the carriersgenerated in the vertical diode D2 due to the avalanche current I2 passthrough only the p⁺-type diffusion region 24 and reach the p⁺⁺-typecontact region 25. In contrast, in the protective element portion, thecarriers generated in the vertical diode D1 due to the avalanche currentI1 pass through the p⁻-type diffusion region 31 whose impurityconcentration is lower than that of the p⁺-type diffusion region 34 andreach the p⁺⁺-type contact region 32. The operation resistance of thevertical diode D1 of the protective element portion therefore becomeshigher than the operation resistance of the vertical diode D2 of thecircuit portion. The slope of the avalanche current I1 between the firstvoltage Vbv1 and the second voltage Vt1 of the I-V waveform w1 of theprotective element portion thereby becomes more gradual than the slopeof the avalanche current I2 between the first voltage Vbv2 and thesecond voltage Vt2 of the I-V waveform w2 of the circuit portion. Withapplied voltages equal to or higher than the breakdown voltages Vbv1 andVbv2, the increased amount of the avalanche current I1 of the verticaldiode D1 of the protective element portion becomes smaller than theincreased amount of the avalanche current I2 of the vertical diode D2 ofthe circuit portion.

The second point is as follows. In the protective element portion,different from the circuit portion, the n⁺-type diffusion region 33 isarranged at the position between the p⁺-type diffusion region 34 and thep⁺⁺-type contact region 32. The pn-junction between the p⁻-typediffusion region 31 and the n⁺-type diffusion region 33 is thereforepresent in the vicinity of the route for a large portion of theavalanche current I1 flowing through the protective element portion toflow into the wiring layer 35. The pn-junction between the p⁻-typediffusion region 31 and the n⁺-type diffusion region 33 tends to beforward-biased due to the avalanche current I1 and, with the influenceof the high operation resistance of the vertical diode D1 in addition,the parasitic bipolar element T1 of the protective element portion moreeasily snaps back than the parasitic bipolar element T2 of the circuitportion. The current It1 flowing at the start of the snapping back ofthe parasitic bipolar element T1 of the protective element portion issmaller than the current It2 flowing at the start of the snapping backof the parasitic bipolar element T2 of the circuit portion (It1<It2). Inthis case, the second voltage Vt1 for the parasitic bipolar element T1of the protective element portion to start snapping back (hereinafter,referred to as “snapback start voltage”) is set to be lower than thesecond voltage Vt2 for the parasitic bipolar element T2 of the circuitportion to start snapping back (hereinafter, referred to as “snapbackstart voltage”) (Vt1<Vt2). Adjustment of the snapback start voltages Vt1and Vt2 can be realized by adjusting the resistive component R1 by thep⁻-type diffusion region 31. For example, the adjustment of the snapbackstart voltages Vt1 and Vt2 may be executed by adjusting the impurityconcentration of the p⁻-type diffusion region 31 in the protectiveelement portion, may be executed by adjusting a distance x1 from thep⁺-type diffusion region 34 to the p⁺⁺-type contact region 32, may beexecuted by adjusting the distance from the p⁺-type diffusion region 34to the n⁺-type diffusion region 33, or may be executed by jointlyadjusting these conditions.

The circuit portion and the protective element portion having the aboveproperties are arranged in a single semiconductor substrate. In a casewhere the surge voltage intrudes from the VCC terminal, when the voltageapplied to the circuit portion is increased up to the snapback startvoltage Vt1 of the parasitic bipolar element T1 of the protectiveelement, the parasitic bipolar element T1 snaps back and the surgecurrent is absorbed by the protective element portion. Even when thesurge voltage intrudes from the VCC terminal, the parasitic bipolarelement T2 of the circuit portion does not snap back. Even when thewidth of the contact hole 28 b constituting the contact portion 28 abetween the n⁺-type source region 22 and the wiring layer of thehorizontal n-channel MOSFET 20 is reduced due to size reductions, nocurrent concentrates at the contact hole 28 b and no breakdown thereforeoccurs. On the other hand, in the protective element portion, when thefootprint of the p⁻-type diffusion region 31 is ensured to besubstantially the same as that of the p⁺-type diffusion region 131 ofthe traditional case (see FIG. 13), more of the contact holes 36 b and37 b, or one contact hole 36 b and one contact hole 37 b each having alarge width, constituting the contact portions 36 a and 37 a in contactwith the wiring layer 35 may be arranged. The breakdown current of eachof the contact holes 36 b and 37 b may thereby be increased, the contactholes 36 b and 37 b are therefore not rapidly broken by the snappingback of the parasitic bipolar element T1 of the protective elementportion, and the breakdown current amount of the protective elementportion may be improved. The surge tolerance of the power IC maytherefore be improved even when size reduction is facilitated.

As described, according to the first embodiment, the operationresistance of the vertical diode of the protective element portion maybe configured to be higher than the operation resistance of the verticaldiode of the circuit portion by providing the p⁺-type diffusion regionthat penetrates the p⁻-type diffusion region in the depth direction ofthe protective element portion and whose depth is equal to or largerthan that of the p⁻-type diffusion region, and by providing the n⁺-typediffusion region at the GND potential between the p⁺-type diffusionregion and the p⁺⁺-type contact region. A surge current may thereby beabsorbed by the protective element portion when a surge voltage isapplied. Concentration of the surge current may be suppressed at thecontact portion between the n⁺-type source region and the wiring layerof the horizontal re-channel MOSFET of the circuit portion even when thewidth of the contact hole constituting the contact portion between then⁺-type source region and the wiring layer of the horizontal n-channelMOSFET is reduced due to size reductions. The surge tolerance of theoverall power IC may be increased.

According to the first embodiment, the diffusion regions of theprotective element portion may be formed concurrently with the diffusionregions of the circuit portion having the same impurity concentrationsand the same depths as those of the above diffusion regions at the sameimpurity implantation and impurity diffusion step, and no new steptherefore needs to be added, enabling increases in cost to besuppressed. According to the first embodiment, the protective elementportion and the circuit portion have the same diffusion layerconfiguration by concurrently forming the diffusion regions of theprotective element portion and the diffusion regions of the circuitportion at the same impurity implantation and impurity diffusion step,and variation of the snapback start current of the parasitic bipolarelement due to process variation tends to be the same in the protectiveelement portion and the circuit portion. The balance of the magnituderelation of the currents each flowing at the start of the snapping backof the parasitic bipolar element is therefore maintained in theprotective element portion and the circuit portion, and stableprotection operation is enabled against process variation.

A structure of a semiconductor device according to a second embodimentwill be described. FIG. 5 is a cross-sectional diagram of a structure ofthe semiconductor device according to the second embodiment. FIG. 5depicts a state during the operation of the semiconductor deviceaccording to the second embodiment (similarly in FIG. 6A, and FIGS. 11and 12). The semiconductor device according to the second embodimentdiffers from the semiconductor device according to the first embodimentin that a width x11 of a p⁺-type diffusion region 44 constituting thevertical diode D2 in the circuit portion is partially and inwardlyincreased. For example, the width x11 of the p⁺-type diffusion region 44is large to the extent that the width x11 reaches the n⁺-type sourceregion 22 from a vicinity of the outer periphery of the p⁻-type baseregion 21, in the portion thereof that faces the n⁺-type source region22 of the horizontal n-channel MOSFET 20. The p⁺-type diffusion region44 may be arranged to overlap a portion of the n⁺-type source region 22.The width x12 of the p⁺⁺-type contact region 45 selectively providedinside the p⁺-type diffusion region 44 may be increased corresponding tothe width x11 of the p⁺-type diffusion region 44. The p⁺⁺-type contactregion 45 may be in contact with the n⁺-type source region 22.

Of the avalanche current I2, the current I2 a flowing toward the n⁺-typesource region 22 side and passing through the low resistance p⁺-typediffusion region 44 may be increased by increasing the width x11 of thep⁺-type diffusion region 44 even when the region having the carriersgenerated therein spreads out due to an increase of the avalanchecurrent I2 generated in a case where the vertical diode D2 breakdowns.An effect is therefore achieved that the current It2 for the parasiticbipolar element T2 of the circuit portion to start snapping back isincreased and the snapback start voltage Vt2 of the parasitic bipolarelement T2 of the circuit portion is increased (see FIG. 4).Establishment of a configuration may thereby be facilitated for theparasitic bipolar element T1 of the protective element portion to snapback sooner than the parasitic bipolar element T2 of the circuit portionwhen a surge voltage intrudes from the VCC terminal, and the degree offreedom of the design of the protective element portion is improved.

As described, according to the second embodiment, effects identical tothose of the first embodiment may obtained.

A structure of a semiconductor device according to a third embodimentwill be described. FIGS. 6A and 6B are cross-sectional diagrams of astructure of the semiconductor device according to the third embodiment.FIGS. 6A and 6B depict the cross-sectional structure of the protectiveelement portion and do not depict the circuit portion or the outputstage portion that are formed on the same semiconductor substrate asthat of the protective element portion. The configurations of thecircuit portion and the output stage portion of the semiconductor deviceaccording to the third embodiment are same as those of the semiconductordevice according to the first embodiment (see FIG. 1). Theconfigurations of the circuit portion and the output stage portion ofthe semiconductor device according to the third embodiment may be sameas those of the semiconductor device according to the second embodiment(see FIG. 5). The semiconductor device according to the third embodimentdiffers from the semiconductor device according to the first embodimentin that the n⁺-type diffusion region 33 is arranged inside each of thep⁺-type diffusion regions 51 and 52 each constituting the vertical diodeD1 in the protective element portion. The p⁺⁺-type contact region 32arranged in a substantially central portion of the p⁻-type diffusionregion 31 may be arranged away from the p⁺-type diffusion region 51(FIG. 6A) or may be arranged inside the p⁺-type diffusion region 52(FIG. 6B).

The resistive component R1 by the p⁻-type diffusion region 31 andcorresponding to the distance from the point of the breakdown of thevertical diode D1 to the p⁺⁺-type contact region 32 may be reduced byarranging the n⁺-type diffusion region 33 in the p⁺-type diffusionregion 51 as depicted in FIG. 6A. The current It1 flowing at the startof the snapping back of the parasitic bipolar element of the protectiveelement portion may therefore be increased corresponding to thereduction amount of the resistive component R1 by the p⁻-type diffusionregion 31. The snapback start voltage Vt1 of the parasitic bipolarelement of the protective element portion may be increased correspondingto the reduction amount of the resistive component R1 by the p⁻-typediffusion region 31. Malfunction such as the snapping back of theparasitic bipolar element of the protective element portion due to noisemay thereby be avoided (see FIG. 4). Noise is, for example, an abnormalvoltage that is a low voltage compared to a surge voltage and that maycause malfunction of the IC. The adjustment of the snapback startvoltage (the second voltage) Vt1 may be executed by adjusting theimpurity concentration of the p⁻-type diffusion region 31, may beexecuted by adjusting the distance from the p⁺-type diffusion region 51to the p⁺⁺-type contact region 32, or may be executed by jointlyadjusting these conditions, in the protective element portion.

As depicted in FIG. 6B, the p⁺-type diffusion region 52 may be arrangedto substantially overlap the p⁻-type diffusion region 31, and thep⁺⁺-type contact region 32 and the n⁺-type diffusion region 33 may bearranged in the p⁺-type diffusion region 52. FIG. 6B depicts the p⁺-typediffusion region 52 whose width is large to the extent to overlap withboth corner portions 31 a of the p⁻-type diffusion region 31. Theresistive component (not depicted) by the p⁻-type diffusion region 31may thereby be further reduced and malfunction due to noise may beavoided. The adjustment of the snapback start voltage Vt1 may beexecuted by adjusting the impurity concentration of each of the p⁻-typediffusion region 31 and the p⁺-type diffusion region 52 in theprotective element portion.

As described, according to the third embodiment, effects identical tothose of the first and second embodiments may be obtained.

A structure of a semiconductor device according to a fourth embodimentwill be described. FIG. 7 is a cross-sectional diagram of a structure ofthe semiconductor device according to the fourth embodiment. FIG. 7depicts the cross-sectional structure of the protective element portionin FIG. 8 and does not depict the circuit portion or the output stageportion that are formed on the same semiconductor substrate as that ofthe protective element portion. FIG. 8 is a plan diagram of the planarlayout of the protective element portion of the semiconductor deviceaccording to the fourth embodiment. FIG. 8 does not depict the planarlayouts of the circuit portion and the output stage portion (the same isapplied to FIG. 20). FIG. 9 is a characteristics diagram of the snapbackproperty of the protective element portion of the semiconductor deviceaccording to the fourth embodiment. The configurations of the circuitportion and the output stage portion of the semiconductor deviceaccording to the fourth embodiment are same as those of thesemiconductor device according to the first embodiment (see FIG. 1). Thesemiconductor device according to the fourth embodiment differs from thesemiconductor device according to the first embodiment in that thestructure of the protective element portion is configured to besubstantially same as the structure of the circuit portion.

For example, as depicted in FIGS. 7 and 8, the arrangement is differentfrom that of the first embodiment with respect to a p⁺⁺-type contactregion 62 and an n⁺-type diffusion region 63 in contact with the wiringlayer 35 connected to the GND terminal in the protective elementportion. For example, the n⁺-type diffusion region 63 is arranged in asubstantially central portion of the n⁻-type diffusion region 31. Thep⁺-type diffusion region 34 constituting the vertical diode D1 isarranged in a vicinity of the periphery of the p⁻-type diffusion region31, to be away from the n⁺-type diffusion region 63 and to surround theperiphery of the n⁺-type diffusion region 63. The p⁺⁺-type contactregion 62 is arranged in the p⁺-type diffusion region 34. Referencenumerals “66 a” and “67 a” denote contact portions of the p⁺⁺-typecontact region 62 and the n⁺-type diffusion region 63, with the wiringlayer 35. Reference numerals “66 b” and “67 b” denote contact holesrespectively for the p⁺⁺-type contact region 62 and the n⁺-typediffusion region 63 to be in contact with the wiring layer 35 (blackrectangular portions in FIG. 8).

As described, the p⁺⁺-type contact region 62, the n⁺-type diffusionregion 63, and the p⁺-type diffusion region 34 of the protective elementportion are arranged similarly to the p⁺⁺-type contact region 25, then⁺-type source region 22, and the p⁺-type diffusion region 24 of thecircuit portion. As depicted in FIG. 9, the current It1 and the snapbackstart voltage Vt1 at the start of the snapping back of the parasiticbipolar element T1 of the protective element portion may be adjusted byadjusting a distance x21 from the p⁺-type diffusion region 34 to then⁺-type diffusion region 63 of the protective element portion. Forexample, the current It1 flowing at the start of the snapping back ofthe parasitic bipolar element T1 of the protective element portion isreduced and the snapping back tends to occur as the distance x21 fromthe p⁺-type diffusion region 34 to the n⁺-type diffusion region 63 ofthe protective element portion is increased. Similar to the firstembodiment, the parasitic bipolar element T1 of the protective elementportion may be caused to snap back sooner than the parasitic bipolarelement T2 of the circuit portion by adjusting the distance x21 from thep⁺-type diffusion region 34 to the n⁺-type diffusion region 63 of theprotective element portion (see FIG. 4). For example, the distance x21from the p⁺-type diffusion region 34 to the n⁺-type diffusion region 63of the protective element portion merely has to be configured to belarger than a distance x2 from the p⁺-type diffusion region 24 to then⁺-type source region 22 of the circuit portion (see FIG. 1) (x21>x2).The adjustment of the snapback start voltage Vt1 may be executed byadjusting the impurity concentration of the p⁻-type diffusion region 31in the protective element portion.

The configuration of the circuit portion may be set to be the sameconfiguration as that of the circuit portion of the semiconductor deviceaccording to the second embodiment (see FIG. 5, x2≤0).

As described, according to the fourth embodiment, effects identical tothose of the first and second embodiments may be obtained.

A structure of a semiconductor device according to a fifth embodimentwill be described. FIGS. 10A, 10B, 10C, 10D, and 10E are cross-sectionaldiagrams of a structure of the semiconductor device according to thefifth embodiment. FIGS. 10A to 10E depict the cross-sectional structureof the protective element portion and do not depict the circuit portionor the output stage portion that are formed on the same semiconductorsubstrate as that of the protective element portion. The configurationsof the circuit portion and the output stage portion of the semiconductordevice according to the fifth embodiment are same as those of thesemiconductor device according to the first embodiment (see FIG. 1). Theconfigurations of the circuit portion and the output stage portion ofthe semiconductor device according to the fifth embodiment may be sameas those of the semiconductor device according to the second embodiment(see FIG. 5). The semiconductor device according to the fifth embodimentdiffers from the semiconductor device according to the first embodimentin that the depth of the p⁺-type diffusion region 71 constituting thevertical diode D1 in the protective element portion is set to be equalto the depth of the p⁻-type diffusion region 31 (FIG. 10A). In the fifthembodiment, the point of the breakdown of the vertical diode D1 of theprotective element portion is a pn-junction between the p⁺-typediffusion region 71 and the n⁻-type epitaxial layer 2.

The time period of the heat treatment for diffusing the impurity may bereduced to form the p⁺-type diffusion region 71 by setting the depth ofthe p⁺-type diffusion region 71 to be substantially equal to the depthof the p⁻-type diffusion region 31 to the extent that the avalanchebreakdown occurs in the bottom portion of the p⁺-type diffusion region71. Diffusion in the lateral direction (the direction parallel to thefront surface of the base substrate) of the p⁺-type diffusion region 71may thereby be suppressed, this is therefore advantageous for sidereductions of the circuit, and the cost may be suppressed. Aconfiguration may be employed to have the depths of the p⁺-typediffusion regions 72 to 74 each constituting the point of the avalanchebreakdown in the protective element portion configured to be equal tothe depth of the p⁻-type diffusion region 31 by applying the fifthembodiment to the third and the fourth embodiments (FIG. 10B to FIG.10D). FIGS. 10B and 10C each depict a case where the fifth embodiment isapplied to the semiconductor device according to the third embodiment(see FIGS. 6A and 6B). FIG. 10D depicts a case where the fifthembodiment is applied to the semiconductor device according to thefourth embodiment (see FIG. 7).

FIG. 10E depicts a modification of FIG. 10A. In the modificationdepicted in FIG. 10E, the depth of the p⁺-type diffusion region 71 isslightly shallower than the depth of the p⁻-type diffusion region 31. Inthis case, an effect identical to that of the configuration depicted inFIG. 10A is achieved by forming the p⁺-type diffusion region 71 suchthat the point of the avalanche breakdown of the protective elementportion is positioned at the bottom of the p⁺-type diffusion region 71.The depth of the p⁺-type diffusion region 71 merely has to be a depthwith which the breakdown voltage of the protective element is determinedby the bottom portion of the p⁺-type diffusion region 71.

In FIGS. 10B, 10C, and 10D, similarly, the depth of the p⁺-typediffusion region 71 may be slightly shallower than the depth of thep⁻-type diffusion region 31.

As described, according to the fifth embodiment, effects identical tothose of the first to fourth embodiments may be obtained.

A structure of a semiconductor device according to a sixth embodimentwill be described. FIG. 11 is a cross-sectional diagram of a structureof the semiconductor device according to the sixth embodiment. FIG. 12is a cross-sectional diagram of another example of a structure of thesemiconductor device according to the sixth embodiment. Theconfigurations of the circuit portion and the output stage portion ofthe semiconductor device according to the sixth embodiment are same asthose of the semiconductor device according to the first embodiment. Thesemiconductor device according to the sixth embodiment differs from thesemiconductor device according to the first embodiment in that theprotective element portion does not have any p⁺-type diffusion regionprovided therein and the protective element portion includes thep⁺⁺-type contact region (the sixth semiconductor region) 32, the n⁺-typediffusion region 33, and a p⁺-type diffusion region (a fourthsemiconductor region) 81 constituting the vertical diode D1.

For example, as depicted in FIG. 11, in the protective element portion,the p⁺-type diffusion region 81 is selectively provided away from thep⁻-type base region 21 of the circuit portion in the surface layer ofthe front surface of the base substrate. The p⁺⁺-type contact region 32and the n⁺-type diffusion region 33 are each selectively provided insidethe p⁺-type diffusion region 81. The p⁺⁺-type contact region 32 isarranged in a substantially central portion of the p⁺-type diffusionregion 81. For the snapback property of the parasitic bipolar element T2of the circuit portion, the parasitic bipolar element T1 of theprotective element portion merely has to have the predetermined snapbackproperty (see FIG. 4), and the p⁺⁺-type contact region 32 may be omitteddepending on the impurity concentration of the p⁺-type diffusion region81. In this case, a contact hole 36 b of the p⁺-type diffusion region 81and constituting a contact portion in contact with the wiring layer isformed in a substantially central portion surrounded by the n⁺-typediffusion region 33. The n⁺-type diffusion region 33 is arranged in asubstantially rectangular ring planar layout to be away from thep⁺⁺-type contact region 32 and to surround the periphery of the p⁺⁺-typecontact region 32. The protective element portion has the parasiticbipolar element T1 formed therein that includes the n⁺-type diffusionregion 33, the p⁺-type diffusion region 81, and the n⁻-type epitaxiallayer 2.

Preferably, the depths of the p⁺⁺-type contact region 32, the n⁺-typediffusion region 33, and the p⁺-type diffusion region 81 are, forexample, respectively equal to the depths of the p⁺⁺-type contact region25, the n⁺-type source region 22, and the p⁺-type diffusion region 24 ofthe circuit portion. The reason for this is that the diffusion regionsof the protective element portion can be formed at the same impurityimplantation and impurity diffusion step (the impurity implantation andimpurity diffusion process) as that for the diffusion regions arrangedin the circuit portion, whose conductivity type and the impurityconcentration are same as those of the above diffusion regions.

When this configuration is employed, the corner portion (the lower sideouter circumferential end) 81 a of the p⁺-type diffusion region 81 isthe point of the breakdown of the vertical diode D2. Similar to thefirst embodiment, the parasitic bipolar element T1 of the protectiveelement portion may therefore be caused to snap back sooner than theparasitic bipolar element T2 of the circuit portion by adjusting adistance x31 from the corner portion 81 a of the p⁺-type diffusionregion 81 to the p⁺⁺-type contact region 32 (see FIG. 4). For example,the distance x31 from the corner portion 81 a of the p⁺-type diffusionregion 81 to the p⁺⁺-type contact region 32 merely has to be configuredto be larger than the distance x2 from the p⁺-type diffusion region 24to the n⁺-type source region 22 of the circuit portion (x31>x2).

Compared to the circuit portion of FIG. 11 and the protective elementportion of FIG. 1, the protective element portion of FIG. 11 has noelectric field alleviation effect of the p⁻-type diffusion region andtherefore tends to break down. A relation Vbv1<Vbv2 therefore holdsbetween the breakdown voltage Vbv1 of the protective element portion andthe breakdown voltage Vbv2 of the circuit portion. The snapback startvoltage Vt1 of the protective element portion is more easily adjusted tobe a value smaller than the snapback start voltage Vt2 of the circuitportion compared to a case where the adjustment of only the operationresistance is executed. The process step to form the p⁻-type diffusionregion in the protective element portion may be omitted, and the numberof process steps may therefore be reduced in a case, for example, wherethe diffusion regions of the protective element portion and thediffusion regions of the circuit portion are formed using separateprocess steps and thus, the cost may be suppressed. The adjustment ofthe snapback start voltage Vt1 may be executed by adjusting the impurityconcentration of the p⁺-type diffusion region 81 in the protectiveelement portion.

As depicted in FIG. 12, the depth of a p⁺-type diffusion region 82constituting the vertical diode D1 in the protective element portion andthe depth of a p⁺-type diffusion region 83 constituting the verticaldiode D2 in the circuit portion may be set to be equal to the depth ofthe p⁻-type base region 21 in the circuit portion.

As described, according to the sixth embodiment, effects identical tothose of the first to fifth embodiments may be obtained even when nop⁻-type diffusion region is provided in the protective element portion.

A structure of a semiconductor device according to a seventh embodimentwill be described. FIG. 14 is a cross-sectional diagram of the structureof the semiconductor device according to the seventh embodiment. FIG. 14depicts the cross-sectional structure taken along a cutting line B-B′ inFIG. 15. FIG. 15 is a planar diagram of the planar layout of thesemiconductor device according to the seventh embodiment. FIG. 15depicts a case where plural unit cells of the horizontal n-channelMOSFET 20 of the circuit portion are arranged. The semiconductor deviceaccording to the seventh embodiment differs from the semiconductordevice according to the sixth embodiment in that an n-type or a p-typediffusion region (a ninth semiconductor region) 91 is provided betweenthe p⁺-type diffusion region 82 constituting the vertical diode D1 inthe protective element portion and the n⁺-type diffusion region 33 inthe p⁺-type diffusion region 82. The diffusion region 91 has a functionof adjusting the snapback start voltage Vt1 of the parasitic bipolarelement T1 of the protective element 30.

For example, as depicted in FIG. 14, the diffusion region 91 is providedin the p⁺-type diffusion region 82 to cover the entire lower portion(the portion on the n⁺-type supporting substrate 1 side) of the n⁺-typediffusion region 33. The diffusion region 91 is arranged away from thep⁺⁺-type contact region 32. The diffusion region 91 is an n-type or ap-type diffusion region formed by introducing an n-type impurity or ap-type impurity into the p⁺-type diffusion region 82 and is formed by,for example, ion implantation and heat treatment for activation. Whenthe diffusion region 91 is formed by introducing a p-type impurity intothe p⁺-type diffusion region 82, the p-type diffusion region 91 isformed having a p-type impurity concentration that is higher than thatof the p⁺-type diffusion region 82. The snapback start voltage Vt1 ofthe parasitic bipolar element T1 of the protective element 30 becomeshigher compared to a case where the diffusion region 91 is not provided,as the p-type impurity concentration of the p-type diffusion region 91becomes higher.

On the other hand, when the diffusion region 91 is formed by introducingan n-type impurity into the p⁺-type diffusion region 82, the diffusionregion 91 is formed having an n-type impurity concentration that ishigher than that of the p⁺-type diffusion region 82. In this case, theconductivity type of the diffusion region 91 is determined by the doseamount of the n-type impurity introduced into the p⁺-type diffusionregion 82. When the n-type impurity concentration of the diffusionregion 91 is lower than the p-type impurity concentration of the p⁺-typediffusion region 82, a p-type diffusion region 91 is formed having animpurity concentration that is lower than that of the p⁺-type diffusionregion 82. When the n-type impurity concentration of the diffusionregion 91 is higher than the p-type impurity concentration of thep⁺-type diffusion region 82, a portion of the p⁺-type diffusion region82 inverts to have the n-type and an n-type diffusion region 91 isformed. The snapback start voltage Vt1 of the parasitic bipolar elementT1 of the protective element 30 becomes lower compared to a case wherethe diffusion region 91 is not provided, as the n-type impurityconcentration of the n-type diffusion region 91 becomes higher.

As depicted in FIG. 15, the n⁺-type diffusion region 33 may be arrangedin, for example, a substantially straight line planar layout. Thep⁺-type contact region 32 may be arranged along, for example, a straightline that passes through the n⁺-type diffusion region 33 in parallel tothe longitudinal direction of the n⁺-type diffusion region 33 (adirection to extend in the straight line). The diffusion region 91 isarranged in, for example, a substantially straight line planar layoutthat covers the periphery of the n⁺-type diffusion region 33. The pluralcontact holes 37 b each constituting the contact portion 37 a (see FIG.14) between the n⁺-type diffusion region 33 and the wiring layer (notdepicted) each have, for example, a substantially rectangular planarshape and are provided to be scattered along the longitudinal directionof the n⁺-type diffusion region 33. The contact hole 36 b constitutingthe contact portion between the p⁺⁺-type contact region 32 and thewiring layer has, for example, a substantially rectangular planar shapeand one contact hole 36 b is provided. The configurations of the circuitportion and the output stage portion are same as those of the sixthembodiment.

An operation of the protective element portion will be described. FIG.16 is a characteristics diagram of the snapback property of thesemiconductor device according to the seventh embodiment. FIG. 16depicts the current-voltage (I-V) waveforms of Examples 1 and 2, andComparative Example taken when the voltage of the VCC terminal isincreased due to the intrusion of the surge voltage from the VCCterminal. Comparative Example 1 is the protective element 30 that hasthe n-type diffusion region 91 provided therein according to theconfiguration of the semiconductor device according to the seventhembodiment. Example 2 is the protective element 30 that has the p-typediffusion region 91 provided therein according to the configuration ofthe semiconductor device according to the seventh embodiment.Comparative Example has the same configuration as those of Examples 1and 2 except that the diffusion region 91 is not provided therein, andcorresponds to, for example, the protective element 30 of the sixthembodiment.

As depicted in FIG. 16, a snapback start voltage Vt11 of the parasiticbipolar element T1 of Example 1 is lower than the snapback start voltageVt1 of the parasitic bipolar element T1 of Comparative Example. Asnapback start voltage Vt12 of the parasitic bipolar element T1 ofExample 2 is higher than the snapback start voltage Vt1 of the parasiticbipolar element T1 of Comparative Example. The snapback start voltageVt1 of the parasitic bipolar element T1 of the protective element 30 maytherefore be adjusted by adjusting the n-type impurity concentration orthe p-type impurity concentration of the diffusion region 91. Theadjustable range thereof is a range X that is equal to or higher thanthe snapback start voltage Vt11 of the parasitic bipolar element T1 ofExample 1 and equal to or lower than the snapback start voltage Vt12 ofthe parasitic bipolar element T1 of Example 2.

The p⁺-type diffusion region 83 may be arranged to overlap a portion ofthe n⁺-type source region 22 of the horizontal n-channel MOSFET 20 byincreasing the width of the p⁺-type diffusion region 83 constituting thevertical diode D2 in the circuit portion by applying the secondembodiment to the seventh embodiment. Similar to the second embodiment,the parasitic operation of the horizontal n-channel MOSFET 20 is therebysuppressed and the snapback start voltage Vt2 of the parasitic bipolarelement T2 of the circuit portion becomes high. Thus, the differencebetween the snapback start voltage Vt1 of the parasitic bipolar elementT1 of the protective element 30 and the snapback start voltage Vt2 ofthe parasitic bipolar element T2 of the circuit portion becomes great,and the margin of the parasitic operation may therefore be ensured.

As described, according to the seventh embodiment, effects identical tothose of the first to the sixth embodiments may be obtained. Accordingto the seventh embodiment, the snapback start voltage of the parasiticbipolar element of the protective element may be adjusted by providingthe n-type or the p-type diffusion region to cover the entire lowerportion of the n⁺-type diffusion region in the p⁺-type diffusion regionconstituting the vertical diode in the protective element portion. Thewidth of the p-type diffusion region thereby does not need to be securedto adjust the parasitic resistance of the protective element portion asdescribed in Japanese Laid-Open Patent Publication No. 2010-182727 and atrigger element does not need to be added on the same substrate asdescribed in Japanese Laid-Open Patent Publication No. 2010-157642, toadjust the snapback start voltage of the parasitic bipolar element ofthe protective element. The footprint of the protective element maythereby be reduced, the protective element is therefore easily arrangedat a position close to the point at which the snapping back tends tooccur, and the degree of freedom of the circuit design becomes high. Thedegree of freedom of the circuit design also becomes high when theprotective elements are arranged at plural points.

A structure of a semiconductor device according to an eighth embodimentwill be described. FIG. 17 is a cross-sectional diagram of the structureof the semiconductor device according to the eighth embodiment. FIG. 17depicts the cross-sectional structure taken along a cutting line C-C′ inFIG. 18. FIG. 18 is a planar diagram of the planar layout of thesemiconductor device according to the eighth embodiment. Thesemiconductor device according to the eighth embodiment differs from thesemiconductor device according to the seventh embodiment in that aprotective element 40 including the n-type or p-type diffusion region 91is integrated with the p⁺-type diffusion region 83 that functions as aguard ring in the circuit portion. The protective element 40 is arrangedin the circuit portion by configuring the protective element 40 usingthe vertical diode D2 that is formed in the circuit portion.

For example, as depicted in FIGS. 17 and 18, the n⁺-type diffusionregion 33 is arranged in a substantially straight line planar layoutalong one side of the p⁺-type diffusion region 83 that is arranged in asubstantially rectangular frame planar layout surrounding the peripheryof the horizontal n-channel MOSFET 20. In this case, the p⁺⁺-typecontact region 25 present inside the p⁺-type diffusion region 83 isarranged in, for example, a substantially C-shaped planar layout alongthe other three sides of the p⁺-type diffusion region 83. In the p⁺-typediffusion region 83, a portion 83 b where the n⁺-type diffusion region33 is arranged thereby acts as the protective element 40, and a portion83 a where the p⁺⁺-type contact region 25 is arranged functions as aguard ring.

In the p⁺-type diffusion region 83 (83 b) and away from the p⁺⁺-typecontact region 25, the diffusion region 91 is arranged in, for example,a substantially linear planar layout to cover the periphery of then⁺-type diffusion region 33. The configuration is same as that of theseventh embodiment except for the arrangement of the diffusion region91. Here, although the protective element 40 is integrated with the sideof the p⁺-type diffusion region 83 facing the n⁺-type source region 22of the horizontal n-channel MOSFET 20, the protective element 40 may beintegrated with the other side of the p⁺-type diffusion region 83.Although not depicted, the eighth embodiment is applied to the seventhembodiment, and the protective element 40 arranged in the circuitportion and the protective element of the protective element portionarranged outside the circuit portion (the reference numeral “30” of FIG.14) may concurrently be used.

Even when the protective element 40 including the vertical diode D2 isintegrated with the guard ring as above, the same effect as that of theseventh embodiment is achieved by providing the n-type or p-typediffusion region 91 to cover the entire lower portion of the n⁺-typediffusion region 33. When the parasitic bipolar element T1 of theprotective element 40 and including the n⁺-type diffusion region 33, thep⁺-type diffusion region 83, and the n⁻-type epitaxial layer 2 snapsback, avalanche current flows through the n⁺-type source region 22 ofthe horizontal n-channel MOSFET 20 and the n⁺-type diffusion region 33in the p⁺-type diffusion region 83. Compared to a case where thevertical diode D2 that parasitizes the guard ring to operate is notprovided, since the avalanche current is distributed among the n⁺-typesource region 22 of the horizontal n-channel MOSFET 20 and the p⁺-typediffusion region 83, a higher current may flow.

As described, according to the eighth embodiment, effects identical tothose of the first to the seventh embodiments may be obtained even whenthe protective element is integrated with the p⁺-type diffusion regionthat functions as the guard ring in the circuit portion. According tothe eighth embodiment, size reductions may be facilitated by integratingthe protective element with the p⁺-type diffusion region that functionsas the guard ring in the circuit portion.

A structure of a semiconductor device according to a ninth embodimentwill be described. FIG. 19 is a cross-sectional diagram of the structureof the semiconductor device according to the ninth embodiment. FIG. 19depicts the cross-sectional structure taken along a cutting line D-D′ inFIG. 20. FIG. 20 is a planar diagram of the planar layout of thesemiconductor device according to the ninth embodiment. FIG. 21 is across-sectional diagram of another example of the structure of thesemiconductor device according to the ninth embodiment. Thesemiconductor devices according to the ninth embodiment depicted inFIGS. 20 and 21 are semiconductor devices that are formed by applyingthe seventh embodiment respectively to the first and the sixthembodiments.

For example, an n-type or p-type diffusion region 92 is arranged in asubstantially rectangular ring planar layout along the n⁺-type diffusionregion 33 that is arranged in a substantially rectangular ring planarlayout surrounding the periphery of the p⁺⁺-type contact region 32 ofthe protective element portion. Similar to the seventh embodiment, thediffusion region 92 is provided to cover the entire lower portion of then⁺-type diffusion region 33. Similar to the seventh embodiment, thesnapback start voltage Vt1 of the parasitic bipolar element T1 of theprotective element 30 may be adjusted by adjusting the n-type impurityconcentration and the p-type impurity concentration of the diffusionregion 92.

As described, according to the ninth embodiment, effects identical tothose of the first, sixth, and seventh embodiments may be obtained.

A structure of a semiconductor device according to a tenth embodimentwill be described. FIG. 22 is a cross-sectional diagram of a structureof the semiconductor device according to the tenth embodiment. FIG. 23is a cross-sectional diagram of another example of a structure of thesemiconductor device according to the tenth embodiment. Thesemiconductor devices according to the tenth embodiment depicted inFIGS. 22 and 23 are semiconductor devices respectively formed byapplying the eighth embodiment to the first and the second embodiments.

For example, as depicted in FIG. 22, the protective element 40 includingthe n-type or p-type diffusion region 91 similar to that of the eighthembodiment is integrated with a portion 24 b of the p⁺-type diffusionregion 24 that functions as a guard ring in the circuit portion. Theprotective element 40 including the diffusion region 91 is therebyarranged in the circuit portion in addition to the protective element(not depicted) of the protective element portion arranged outside thecircuit portion, and these two protective elements are usedconcurrently. As depicted in FIG. 23, in the p⁺-type diffusion region 44functioning as the guard ring in the circuit portion, the width of aportion 44 b integrated with the protective element 40 may be increasedto overlap a portion of the n⁺-type source region 22 of the horizontaln-channel MOSFET 20.

Here, although the protective element 40 is integrated with the portions24 b and 44 b of the p⁺-type diffusion region 24 facing the n⁺-typesource region 22 of the horizontal n-channel MOSFET 20, the protectiveelement 40 may be integrated with other portions 24 a and 44 a of thep⁺-type diffusion region 24. FIGS. 22 and 23 do not depict thecomponents constituting the protective element portion arranged outsidethe circuit portion, however, the configuration of the protectiveelement portion may be same as that of the first and second embodimentsor may be same as that of the ninth embodiment. When the configurationof the protective element portion arranged outside the circuit portionis set to be same as that of the ninth embodiment, the n-type or p-typediffusion region 91 is arranged in the protective element of theprotective element portion.

As described, according to the tenth embodiment, effects identical tothose of the first, eighth, and ninth embodiment may be obtained.

In the first embodiment and the like, the impurity concentration and thedepth of the p⁻-type diffusion region 31 need to be adjusted to adjustthe snapback start current of the vertical snap diode like theprotective element 30. On the other hand, as described, to reduce themanufacturing cost, it is preferable to concurrently form the p⁻-typediffusion region 31 constituting the protective element 30 of theprotective element portion and the p⁻-type diffusion region 21constituting the horizontal n-channel MOSFET 20 of the circuit portion.In this case, when the impurity concentrations and the depths of thep⁻-type diffusion region 21 and the p⁻-type diffusion region 31 aredetermined prioritizing the property of the horizontal n-channel MOSFET20, the adjustment of the snapback start current of the protectiveelement 30 may be difficult. A semiconductor device will be describedfor which effective protection may be obtained even when the adjustmentof the snapback start current of the protective element 30 is difficult.

A structure of a semiconductor device according to an eleventhembodiment will be described. FIG. 24 is a cross-sectional diagram ofthe structure of the semiconductor device according to the eleventhembodiment. FIG. 24 depicts the cross-sectional structure taken along acutting line E-E′ in FIG. 25. FIG. 25 is a planar diagram of the planarlayout of the semiconductor device according to the eleventh embodiment.FIG. 25 depicts only the protective element portion. The semiconductordevice according to the eleventh embodiment differs from thesemiconductor device according to the first embodiment in that theprotective element portion further includes a protective element (asecond protective element) 50 to be away from the protective element (afirst protective element) 30.

The protective element 50 includes a p⁻-type diffusion region (a tenthsemiconductor region) 51 selectively provided in the surface layer ofthe n⁻-type epitaxial layer 2. The p⁻-type diffusion region 51 isarranged away from the p-type base region 6 of the vertical MOSFET 10 ofthe output stage portion, the p⁻-type diffusion region 21 of the circuitportion, and the p⁻-type diffusion region 31 of the protective element30. A p⁺⁺-type contact region (a twelfth semiconductor region) 52 and ap⁺-type diffusion region (an eleventh semiconductor region) 53 areselectively provided inside the p⁻-type diffusion region 51.

The p⁺⁺-type contact region 52 is connected to the GND terminal throughthe wiring layer 35. One or more contact hole(s) 55 b for the p⁺⁺-typecontact region 52 to constitute a contact portion 55 a in contact withthe wiring layer 35 is/are arranged (FIG. 25). FIG. 25 depicts a statewhere the contact hole 55 b is arranged in plural (black rectangularportions). The depth of the p⁺-type diffusion region 53 may be deeperthan the depth of the p⁻-type diffusion region 51. A vertical diode D3is formed by a pn-junction between the p⁺-type diffusion region 53 andthe n⁻-type epitaxial layer 2.

The avalanche voltage (the breakdown voltage) of the vertical diode D3of the protective element 50 is lower than the avalanche voltage of thevertical diode D1 by the pn-junction between the p⁺-type diffusionregion 34 of the protective element 30 and the n⁻-type epitaxial layer2. For example, an overhang width wa in the lateral direction from thep⁺-type diffusion region 53 of the p⁻-type diffusion region 51 of theprotective element 50 is set to be smaller than an overhang width wb inthe lateral direction from the p⁺-type diffusion region 34 of thep⁻-type diffusion region 31 of the protective element 30. The electricfield alleviation effect of the outer periphery portion of theprotective element 50 is weakened by setting the overhang width wa ofthe p⁻-type diffusion region 51 of the protective element 50 to besmaller than the overhang width wb of the p⁻-type diffusion region 31 ofthe protective element 30. The avalanche voltage of the vertical diodeD3 can thereby be set to be lower than the avalanche voltage of thevertical diode D1.

In this embodiment, the protective element 30 is desirably set such thatthe parasitic bipolar element T1 immediately operates when the breakdownvoltage is exceeded. For example, the distance x1 from the p⁺-typediffusion region 34 to the p⁺⁺-type contact region 32 is set to besufficiently long. In this protective element 30, the snapping backoccurs due to the operation of the parasitic bipolar element T1 and thesnapback start current therefore does not need to be adjusted byadjusting the impurity concentration and the depth of the p⁻-typediffusion region 31.

In this embodiment, the impurity concentration and the depth of thep⁻-type diffusion region 21 may be configured giving priority to thecharacteristics of the elements to be formed in the circuit portion evenwhen the diffusion regions of the p⁻-type diffusion region 31 and thep⁻-type diffusion region 51 of the protective element portion, and thep⁻-type diffusion region 21 of the circuit portion are concurrentlyformed at the same impurity implantation and impurity diffusion step.

FIG. 26 is a characteristics diagram of the snapback property of thesemiconductor device according to the eleventh embodiment. An operationexecuted in a case where the protective element 50 is present alone willbe described with reference to a current-voltage (I-V) waveform w12.When a surge voltage intrudes from the VCC terminal, the voltage of theVCC terminal is thereby increased, and the applied voltage reaches abreakdown voltage Vbv11, the vertical diode D3 runs into a breakdown ata pn-junction between the p⁺-type diffusion region 53 and the n⁻-typeepitaxial layer 2, and a current (an avalanche current) starts to flowtherethrough. Positive carriers (holes) generated in the vertical diodeD3 due to the avalanche current pass through the p⁺-type diffusionregion 53 and flow from the p⁺⁺-type contact region 52 into the GNDterminal through the wiring layer 35. The avalanche current isthereafter increased as the applied voltage is increased due to theoperation resistance of the diode D3.

An operation executed in a case where the protective element 30 ispresent alone will be described with reference to the I-V waveform w13in FIG. 26. When a surge voltage intrudes from the VCC terminal, thevoltage of the VCC terminal is thereby increased, and the appliedvoltage reaches a breakdown voltage Vbv12, the vertical diode D1 breaksdown at the pn-junction between the p⁺-type diffusion region 34 and then⁻-type epitaxial layer 2, and the avalanche current starts to flowtherethrough. Positive carriers (holes) generated in the vertical diodeD1 due to the avalanche current pass through the p⁺-type diffusionregion 34 and the p⁻-type diffusion region 31, and flow from thep⁺⁺-type contact region 32 to the GND terminal through the wiring layer35. The operation resistance of the vertical diode D1 is relatively highdue to the resistive component by the p⁻-type diffusion region 31. Whenthe breakdown occurs, the voltage drop in the p⁻-type diffusion region31 due to the resistive component of the p⁻-type diffusion region 31immediately exceeds the forward voltage of the pn-junction between thep⁻-type diffusion region 31 and the n⁺-type diffusion region 33. Thepn-junction between the p⁻-type diffusion region 31 and the n⁺-typediffusion region 33 is thereby forward-biased and a current that is aportion of the avalanche current flows toward the n⁺-type diffusionregion 33 side. The current flowing toward the n⁺-type diffusion region33 side acts as a base current, and the parasitic bipolar element T1including the n⁺-type diffusion region 33, the p⁻-type diffusion region31, and the n⁻-type epitaxial layer 2 is turned on to snap back. At thistime, the voltage applied to the protective element 30 is reduced to avoltage Vh11 that is lower than the breakdown voltage Vbv11 of thevertical diode D1.

An operation of the overall protective element portion will be describedwith reference to a current-voltage (I-V) waveform w11. When the surgevoltage intrudes from the VCC terminal, the voltage of the VCC terminalis thereby increased, and the applied voltage reaches the breakdownvoltage Vbv11, the vertical diode D3 breaks down and the current (theavalanche current) starts to flow therethrough. When the applied voltagereaches the breakdown voltage Vbv12 due to the operation resistance ofthe vertical diode D3, the vertical diode D1 breaks down at thepn-junction between the p⁺-type diffusion region 34 and the n⁻-typeepitaxial layer 2 and the avalanche current starts to flow. When thebreakdown occurs, the parasitic bipolar element T1 including the n⁺-typediffusion region 33, the p⁻-type diffusion region 31, and the n⁻-typeepitaxial layer 2 is immediately turned on to snap back. At this time,the voltage applied to the protective element 30 is reduced to thevoltage Vh1 that is lower than the breakdown voltage Vbv1 of thevertical diode D1.

The eleventh embodiment is applicable to each of the second to the fifthembodiments in place of the first embodiment.

As described, according to the eleventh embodiment, effects identical tothose of the first to fifth embodiments may be obtained. According tothe eleventh embodiment, the protective element is easily designed evenwhen the impurity concentration and the depth of the p⁻-type diffusionregion are configured giving priority to the characteristics of theelements to be formed in the circuit portion because the snapback startcurrent of the protective element (the snap diode) does not need to beadjusted.

In the description, without limitation to the embodiments, the presentinvention may be variously modified within a scope not departing fromthe spirit of the present invention. For example, although descriptionhas been given taking an example where the vertical MOSFET having atrench gate structure is provided as the semiconductor element for theoutput stage in the above embodiments, any one of various devices suchas a vertical MOSFET having a planar gate structure may be provided asthe semiconductor element for the output stage. The present invention isapplicable to a semiconductor device that has the various devices(elements) constituting the circuit portion and the protective elementprotecting these devices from a surge, included on a singlesemiconductor substrate. The present invention is further implementedeven when the conductivity types (the n type and the p type) aremutually switched.

As a result of active research by the inventors, the following was newlyfound. In the circuit portion of the power IC, the n⁺-type source region122 of the horizontal n-channel MOSFET 120 is formed and the verticalparasitic bipolar element T102 is formed that includes the n⁻-typesemiconductor layer 102, the p⁻-type base region 121, and the n⁺-typesource region 122. Because the n⁺-type source region 122 is electricallyconnected to the GND terminal on the low potential side, when thecurrent flowing through the circuit portion is increased associated withan increase of the surge voltage, the circuit portion diode 127 breaksdown and current (hereafter, referred to as “avalanche current”) I102flows through the p⁺-type diffusion region 124. A current I102 a that isa component of the avalanche current I102 flows onto the n⁺-type sourceregion 122 side to become a base current and the parasitic bipolarelement T102 is turned on and snaps back.

When the parasitic bipolar element T102 snaps back, the impedance of thecircuit portion is rapidly reduced and the current concentrates at then⁺-type source region 122 of the horizontal n-channel MOSFET 120. Then⁺-type source region 122 of the horizontal n-channel MOSFET 120 isformed with a relatively small footprint due to the reduced size of thepower IC and the breakdown current amount is therefore small. Whenbreakdown of the n⁺-type source region 122 occurs in a contact portion128 in contact with the wiring layer due to the concentration of thecurrent at the n⁺-type source region 122, the surge tolerance of theoverall power IC is determined by the current I102 a by which theparasitic bipolar element T102 starts to snap back. The surge toleranceof the overall power IC cannot therefore be effectively increased evenwhen the footprints of the vertical diode 130 and the circuit portiondiode 127 are increased to thereby increase the resistance to breakdownsof these vertical diodes.

To solve the above problems, it is necessary that no breakdown occurs inthe circuit portion even when the parasitic bipolar element T102 of thecircuit portion snaps back, or the parasitic bipolar element T102 of thecircuit portion has to be prevented from snapping back. When nobreakdown occurs in the circuit portion even in a case where theparasitic bipolar element T102 of the circuit portion snaps back, theparasitic bipolar element T102 functions as a protective element whenthe current I102 a equal to or larger than a predetermined current flowsthrough the circuit portion. When the parasitic bipolar element T102 ofthe circuit portion can be caused to function as a protective element asabove, the capacity to absorb the surge current is significantlyimproved relative to a case where the vertical diode 130 and the circuitportion diode 127 are arranged and this is therefore useful forimproving the surge tolerance of the overall power IC.

When the circuit portion is further reduced in size, the width of acontact hole to be the contact portion 128 between the n⁺-type sourceregion 122 and the wiring layer is reduced associated with reduction ofthe footprint of the n⁺-type source region 122 of the horizontaln-channel MOSFET 120, and the breakdown current amount of the contacthole is reduced. Therefore, when the parasitic bipolar element T102 ofthe circuit portion snaps back, the current concentrates at the contactportion 128 between the n⁺-type source region 122 and the wiring layerthereafter, the contact hole tends to breakdown, and the breakdowncurrent amount of the circuit portion is further reduced. It isdifficult to concurrently achieve reductions in the size of the circuitportion and an increase of the breakdown current amount, and it is alsodifficult to improve the surge tolerance of the power IC reduced in sizeand having a configuration whose circuit portion does not breakdown evenwhen the parasitic bipolar element T102 of the circuit portion snapsback.

To improve the surge tolerance of the power IC reduced in size, it isnecessary to reduce the concentration of the current at the circuitportion by significantly improving the capacity to absorb surges by eachof the vertical diode 130 and the circuit portion diode 127 to be theprotective elements, to avoid snapping back of the parasitic bipolarelement T102 of the circuit portion. The patent documents above describetechniques of improving the snapback property of the bipolar elementthat is the protective element, and do not describe any structure thattakes into consideration the relation between the snapback property ofthe parasitic bipolar element formed in the circuit portion of the powerIC and characteristics of the vertical diode that is the protectiveelement. The patent documents above do not describe any method ofimproving the surge tolerance of a power IC that includes a circuitportion having the snapback property or any method of suppressing themanufacturing cost of the power IC.

According to the above invention, the operation resistance of thevertical diode of the protective element portion, that includes thesixth semiconductor region and the semiconductor substrate can be set tobe higher than the operation resistance of the vertical diode of thecircuit portion, that includes the third semiconductor region and thesemiconductor substrate. The protective element portion can therebyabsorb the surge current when the surge voltage is applied.Concentration of the surge current can therefore be suppressed at thecontact portion between the second semiconductor region and the firstelectrode of the circuit portion even when the width of the contact holeto be the contact portion between the second semiconductor region andthe first electrode of the circuit portion is reduced due to thereduction in size. The surge tolerance of the overall semiconductordevice can therefore be increased.

According to the semiconductor device and the method of manufacturing asemiconductor device of the present invention, the circuit portion andthe protective element protecting the circuit portion are included on asingle semiconductor substrate, and effects are achieved in that sizereductions may be facilitated and the surge tolerance may be improved.According to the semiconductor device and the method of manufacturing asemiconductor device of the present invention, an effect is furtherachieved in that the cost of the semiconductor device having a circuitportion and a protective element protecting the circuit portion includedon the same semiconductor substrate may be suppressed.

As described, the semiconductor device and the method of manufacturing asemiconductor device according to the present invention are suitable fora semiconductor device that has devices constituting a circuit portionand a protective element protecting the devices from a surge, includedon a single semiconductor substrate.

Although the invention has been described with respect to a specificembodiment for a complete and clear disclosure, the appended claims arenot to be thus limited but are to be construed as embodying allmodifications and alternative constructions that may occur to oneskilled in the art which fairly fall within the basic teaching hereinset forth.

What is claimed is:
 1. A semiconductor device comprising: a firstsemiconductor region of a second conductivity type selectively providedin a surface layer of a first principal surface of a semiconductorsubstrate of a first conductivity type; an element structure of asemiconductor element provided in the first semiconductor region; asecond semiconductor region of the first conductivity type selectivelyprovided in the first semiconductor region, the second semiconductorregion constituting the element structure of the semiconductor element;a third semiconductor region of the second conductivity type selectivelyprovided to penetrate the first semiconductor region in a depthdirection and to surround the element structure of the semiconductorelement at a depth equal to or deeper than a depth of the firstsemiconductor region, the third semiconductor region having an impurityconcentration that is higher than that of the first semiconductorregion; a fourth semiconductor region of the second conductivity typeselectively provided in the surface layer of the first principal surfaceof the semiconductor substrate to be spaced apart from the firstsemiconductor region; a fifth semiconductor region of the firstconductivity type selectively provided in the fourth semiconductorregion; a sixth semiconductor region of the second conductivity typeselectively provided to penetrate the fourth semiconductor region in thedepth direction and to be at a depth equal to or deeper than a depth ofthe fourth semiconductor region, the sixth semiconductor region havingan impurity concentration that is higher than that of the fourthsemiconductor region; a first electrode that is electrically connectedto the second semiconductor region, the third semiconductor region, thefourth semiconductor region, and the fifth semiconductor region; and asecond electrode that is connected to a second principal surface of thesemiconductor substrate.
 2. The semiconductor device according to claim1, further comprising a seventh semiconductor region of the secondconductivity type selectively provided in the fourth semiconductorregion, the seventh semiconductor region having an impurityconcentration that is higher than that of the fourth semiconductorregion, wherein the first electrode is electrically connected to thefourth semiconductor region through the seventh semiconductor region,and the fifth semiconductor region is arranged between the sixthsemiconductor region and the seventh semiconductor region.
 3. Thesemiconductor device according to claim 1, further comprising a seventhsemiconductor region of the second conductivity type selectivelyprovided in the fourth semiconductor region, the seventh semiconductorregion having an impurity concentration that is higher than that of thefourth semiconductor region, wherein the first electrode is electricallyconnected to the fourth semiconductor region through the seventhsemiconductor region, the seventh semiconductor region is arranged to beaway from the sixth semiconductor region, and the fifth semiconductorregion is selectively provided in the sixth semiconductor region.
 4. Thesemiconductor device according to claim 1, further comprising a seventhsemiconductor region of the second conductivity type selectivelyprovided in the sixth semiconductor region, the seventh semiconductorregion having an impurity concentration that is higher than that of thesixth semiconductor region, wherein the first electrode is electricallyconnected to the fourth semiconductor region through the seventhsemiconductor region, and the fifth semiconductor region is selectivelyprovided in the sixth semiconductor region.
 5. The semiconductor deviceaccording to claim 1, further comprising a seventh semiconductor regionof the second conductivity type selectively provided in the sixthsemiconductor region, the seventh semiconductor region having animpurity concentration that is higher than that of the sixthsemiconductor region, wherein the first electrode is electricallyconnected to the fourth semiconductor region through the seventhsemiconductor region, and the fifth semiconductor region is arranged tobe away from the sixth semiconductor region.
 6. The semiconductor deviceaccording to claim 2, wherein the fifth semiconductor region is arrangedto surround a periphery of the seventh semiconductor region.
 7. Thesemiconductor device according to claim 2, wherein the fifthsemiconductor region is arranged to surround a periphery of the seventhsemiconductor region, and the sixth semiconductor region is arranged tosurround a periphery of the fifth semiconductor region.
 8. Thesemiconductor device according to claim 2, wherein the sixthsemiconductor region is arranged to surround a periphery of the seventhsemiconductor region.
 9. The semiconductor device according to claim 2,wherein the sixth semiconductor region is arranged to surround aperiphery of the fifth semiconductor region.
 10. The semiconductordevice according to claim 1, wherein the sixth semiconductor region hasan impurity concentration and a depth equal to those of the thirdsemiconductor region.
 11. The semiconductor device according to claim 1,wherein the fourth semiconductor region has an impurity concentrationand a depth equal to those of the first semiconductor region.
 12. Thesemiconductor device according to claim 1, wherein a distance from thesixth semiconductor region to a contact portion of the fourthsemiconductor region and the first electrode is configured such that afirst voltage at which a first parasitic bipolar element constituted bythe fifth semiconductor region, the fourth semiconductor region, and thesemiconductor substrate or a second parasitic bipolar elementconstituted by the fifth semiconductor region, the sixth semiconductorregion, and the semiconductor substrate starts to snap back is lowerthan a second voltage at which a third parasitic bipolar elementconstituted by the second semiconductor region, the first semiconductorregion, and the semiconductor substrate starts to snap back.
 13. Thesemiconductor device according to claim 2, wherein a distance from thesixth semiconductor region to the seventh semiconductor region isconfigured such that a first voltage at which a first parasitic bipolarelement constituted by the fifth semiconductor region, the fourthsemiconductor region, and the semiconductor substrate or a secondparasitic bipolar element constituted by the fifth semiconductor region,the sixth semiconductor region, and the semiconductor substrate startsto snap back is lower than a second voltage at which a third parasiticbipolar element constituted by the second semiconductor region, thefirst semiconductor region, and the semiconductor substrate starts tosnap back.
 14. The semiconductor device according to claim 2, wherein adistance from the sixth semiconductor region to the fifth semiconductorregion is configured such that a first voltage at which a firstparasitic bipolar element constituted by the fifth semiconductor region,the fourth semiconductor region, and the semiconductor substrate startsto snap back is lower than a second voltage at which a second parasiticbipolar element constituted by the second semiconductor region, thefirst semiconductor region, and the semiconductor substrate starts tosnap back.
 15. The semiconductor device according to claim 1, whereinthe fourth semiconductor region is configured to have an impurityconcentration such that a first voltage at which a first parasiticbipolar element constituted by the fifth semiconductor region, thefourth semiconductor region, and the semiconductor substrate or a secondparasitic bipolar element constituted by the fifth semiconductor region,the sixth semiconductor region, and the semiconductor substrate startsto snap back is lower than a second voltage at which a third parasiticbipolar element constituted by the second semiconductor region, thefirst semiconductor region, and the semiconductor substrate starts tosnap back.
 16. The semiconductor device according to claim 1, whereinthe element structure of the semiconductor element includes: the secondsemiconductor region; an eighth semiconductor region of the firstconductivity type selectively provided in the first semiconductor regionand away from the second semiconductor region; and a gate electrode thatis provided through a gate insulating film on a surface of the firstsemiconductor region at a portion between the second semiconductorregion and the eighth semiconductor region.
 17. The semiconductor deviceaccording to claim 1, wherein the semiconductor device is provided withthe first semiconductor region and the fourth semiconductor regionformed at a same process step.
 18. The semiconductor device according toclaim 1, wherein the semiconductor device is provided with the thirdsemiconductor region and the sixth semiconductor region formed at a sameprocess step.
 19. The semiconductor device according to claim 1, whereinthe semiconductor device is provided with the second semiconductorregion and the fifth semiconductor region formed at a same process step.20. The semiconductor device according to claim 1, further comprising: atenth semiconductor region of the second conductivity type selectivelyprovided in the surface layer of the first principal surface of thesemiconductor substrate to be away from the first semiconductor regionand the fourth semiconductor region; an eleventh semiconductor region ofthe second conductivity type selectively provided to penetrate the tenthsemiconductor region in the depth direction and to be at a depth equalto or deeper than a depth of the tenth semiconductor region; and atwelfth semiconductor region of the second conductivity type selectivelyprovided in a surface layer of the eleventh semiconductor region, thetwelfth semiconductor region having an impurity concentration that ishigher than that of the eleventh semiconductor region, wherein a firstavalanche voltage of a first diode constituted by the semiconductorsubstrate and the third semiconductor region is higher than a secondavalanche voltage of a second diode constituted by the semiconductorsubstrate and the eleventh semiconductor region.
 21. The semiconductordevice according to claim 20, wherein on a surface of the firstprincipal surface of the semiconductor substrate, a first distancebetween the semiconductor substrate and the sixth semiconductor regionis larger than a second distance between the semiconductor substrate andthe eleventh semiconductor region.